Processor for executing instructions in units that are unrelated to the units in which instructions are read, and a compiler, an optimization apparatus, an assembler, a linker, a debugger and a disassembler for such processor

ABSTRACT

When a branch instruction is decoded by the instruction decoders  409   a˜   409   c , the upper 29 bits of the PC relative value included in the branch instruction are sent to the upper PC calculator  411  and the lower 3 bits are sent to the lower PC calculator  405 . The lower PC calculator  405  adds the lower 3 bits of the PC relative value and the lower 3 bits of the present lower PC  404  and sends the result to the lower PC  404  as the updated lower PC. The upper PC calculator  411  adds the upper 29 bits of the PC relative value, the upper 29 bits of the present upper PC  403 , and a carry that may be received from the lower PC calculator  405 , and sends the result to the upper PC  403  as the updated upper PC.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/045,802,filed Oct. 19, 2001, now U.S. Pat. No. 6,976,250, which is a divisionalof application Ser. No. 09/301,284, filed Apr. 28, 1999, which is nowU.S. Pat. No. 6,880,150, which claims priority of Japanese ApplicationNo. 10-118326, filed Apr. 28, 1998, the contents of which are herebyincorporated by reference.

This application is based on an application No. H10-118326 filed inJapan, the content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a processor for executing instructionsin units that are unrelated to the units in which instructions are read,and a compiler, an optimization apparatus, an assembler, a linker, adebugger and a disassembler for such processor.

2. Description of the Prior Art

Processors conventionally read and execute instructions stored in memoryaccording to a program counter. FIG. 1 is a block diagram showing thebasic construction of an example processor.

The instruction memory 4301 stores four 8-bit instructions as oneinstruction packet.

The program counter 4300 indicates the address of an instruction packetin the instruction memory 4301.

The instruction reading unit 4302 reads the instruction packet indicatedby the program counter 4300 from the instruction memory 4301.

The instruction executing unit 4303 executes all four instructionsincluded in the read instruction packet in one cycle.

In this way, a conventional processor can read an instruction packetthat is indicated by the program counter and can execute fourinstructions in the instruction packet.

The above processor has to execute all of the instructions in the readinstruction packet in one cycle. Accordingly, when one or moreinstructions in an instruction packet cannot be executed due to problemswith computer system resources such as memory or I/O, none of theinstructions in the instruction packet can be executed until suchproblems are resolved. This slows program execution.

SUMMARY OF THE INVENTION

In view of the stated problems, it is a primary object of the presentinvention to provide a processor that executes instructions in unitsthat are unrelated to the units in which instructions are read from aprogram and a program development environment for generating suitableprograms.

This primary object is achieved by a processor for reading instructionsfrom a memory according to a program counter, the memory storinginstructions in one-byte units, and for executing the read instructions,the program counter including a first program counter and a secondprogram counter, the first program counter indicating a storage positionof a processing packet in the memory, the processing packet beingcomposed of an integer number of the one-byte units, the second programcounter indicating a position of processing target instruction in theprocessing packet, the processing target instruction being an operationto be executed by the processor.

With the stated construction, the first program counter indicates astorage position in the memory of a processing packet whose size is aninteger number of bytes. Reads from the memory are performed based onthis first program counter. The second program counter can indicate anyposition of a processing target instruction included in the processingpacket read from the memory. As a result, the instruction(s) to beexecuted can be freely set regardless of the amount of data read in oneread operation. This means that instructions whose word length is not aninteger number of bytes can be executed even when read operations fromthe memory to the processor are performed in units of an integer numberof bytes.

Here, the processor may include a first program counter updating unitand a second program counter updating unit, the second program counterupdating unit incrementing a value of the second program counter inaccordance with an amount of instructions that were executed in apreceding cycle and sending any carry generated in an incrementing tothe first program counter updating unit, and the first program counterupdating unit adding the carry received from the second program counterupdating unit to the value of the first program counter.

With the stated construction, the value of the program counter isincremented by the amount of instructions that have just been executed,so that the program counter can be updated to indicate the firstposition of the instructions to be executed in the next cycle.

Here, the processor may further include: a program counter relativevalue extracting unit for extracting, when an instruction being executedincludes a program counter relative value that is based on an address ofa first instruction executed in a present cycle, the program counterrelative value; and a calculating unit for adding the program counterrelative value to the value of the first program counter and the valueof the second program counter, and setting an addition result as thevalue of the first program counter and the value of the second programcounter.

When the processor executes a branch instruction, the value of theprogram counter is added to a program counter relative value that is adifference in addresses between the present branch instruction and thebranch destination instruction. The result of this addition is then setas the new value of the program counter to have the program counterindicate the branch destination instruction.

Here, the calculating unit may include a first calculating unit and asecond calculating unit, the second calculating unit adding the value ofthe second program counter and lower bits of the program counterrelative value, setting a result of an addition as the value of thesecond program counter, and sending any carry generated in the additionto the first calculating unit, and the first calculating unit adding thevalue of the first program counter, upper bits of the program counterrelative value, and any carry received from the second calculating unit,and setting a result of an addition as the value of the first programcounter.

When the processor executes a branch instruction and the program counterand a program counter relative value are added, a carry generated whencalculating the lower bits is properly considered when calculating theupper bits. In this way, addresses can be calculated with propercontinuity between the calculation of the lower bits and the calculationof the upper bits.

Here, the calculating unit may include a first calculating unit and asecond calculating unit, the second calculating unit adding the value ofthe second program counter and lower bits of the program counterrelative value without generating a carry, and setting a result of anaddition as the value of the second program counter, the firstcalculating unit adding the value of the first program counter and upperbits of the program counter relative value, and setting a result of anaddition as the value of the first program counter.

When the processor executes a branch instruction, calculation of thelower bits of the value of the program counter and the program counterrelative value by the second calculating unit does not generate a carryto the calculation of the upper bits of the value of the program counterand the program counter relative value by the first calculating unit. Asa result, the calculations of the first and second calculators can beperformed independently of one another, so that a simplified hardwareconstruction can be used.

Here, the calculating unit may add the value of the first programcounter and upper bits of the program counter relative value, sets aresult of an addition as the value of the first program counter, andsets lower bits of the program counter relative value as the value ofthe second program counter.

When the processor executes a branch instruction, no calculation usingthe value of the second program counter and the lower bits of theprogram counter relative value is required, so that the processor canexecute branch instructions at a higher speed.

Here, the calculating unit may add the program counter relative valueand a value whose upper bits are the value of the first program counterand lower bits are the value of the second program counter, and setsupper bits of a result of an addition as the value of the first programcounter and lower bits of the result as the second program counter.

When the processor executes a branch instruction, the calculation usingthe value of the program counter and the program counter relative valuecan be performed by a standard calculator. This means the hardwareconstruction of the processor can be simplified.

Here, the processor may further include: a program counter relativevalue extracting unit for extracting, when an executed instructionincludes a program counter relative value that is based on an address ofthe executed instruction, the program counter relative value; a programcounter amending unit for amending the value of the first programcounter and the value of the second program counter to indicate anaddress of the executed instruction; and a calculating unit for addingthe program counter relative value, the value of the first programcounter, and the value of the second program counter, and setting aresult of an addition as the value of the first program counter and thevalue of the second program counter.

The program counter relative value is the difference in addressesbetween a branch instruction and the branch destination instruction, sothat it will not be necessary to change the program counter relativevalue even when there is a change in the boundaries marking whichinstructions in the program will be executed in parallel.

Here, the processor may further include: a program counter relativevalue calculating instruction decoding unit for decoding a programcounter relative value calculating instruction that performs an additionusing a program counter relative value and one of (a) a value of theprogram counter stored in a register, and (b) the value of the firstprogram counter and the value of the second program counter; acalculating unit for performing the addition indicated by the programcounter relative value calculating instruction to generate an additionresult; and a program counter value updating unit for storing theaddition result in one of (a) the register, and (b) the first programcounter and the second program counter.

With the stated construction, it is possible to use an instruction thatindicates a calculation using the value of the program counter and aprogram counter relative value in place of an instruction that storesthe absolute address of a function into a register. A program counterrelative value has a shorter bit width that the absolute address of aninstruction, so that the overall code size can be reduced. When usingPIC codes where the addresses of instructions in memory are onlydetermined when the program is executed, absolute addresses cannot beused, so that calculation instructions that use the program counter anda program counter relative value are essential.

Here, the first program counter may indicate a memory address, thememory address being a storage position in the memory of a processingpacket that is given by bit shifting the value in the first programcounter by log₂n bits in a leftward direction, n being a length of aprocessing packet in bytes.

With the stated construction, while separate addresses are assigned toeach one-byte storage packet in the memory, the value of the firstprogram counter corresponds with the address of a processing packet inthe memory. As a result, the processor can easily specify a processingpacket in the memory.

Here, the processor may further include: an instruction buffer fortemporarily storing instructions; and an instruction reading unit fortransferring instructions with a minimum transfer size of one one-byteunit from the memory to the instruction buffer, in accordance withavailable space in the instruction buffer but regardless of a size of aprocessing packet.

With the stated construction, the amount of data read by the processorfrom the memory in one read operation can be freely set, so that theconstruction in the processor for reading instructions can be madehighly flexible.

The stated primary object can also be achieved by an instructionsequence optimizing apparatus, for generating optimized code from aninstruction sequence, including: an address assigning unit forestimating a size of each instruction in the instruction sequence andassigning an address to each instruction, upper bits of each addressindicating a memory address at which a processing packet is stored andlower bits of each address indicating a processing target instruction inthe processing packet; a label detecting unit (1) for detecting a label,which should be resolved by an address of a specified instruction, fromthe instruction sequence, and obtaining the address of the specifiedinstruction, and (2) for detecting a label, which should be resolved bya difference in addresses of two specified instructions, from theinstruction sequence, and obtaining the addresses of the two specifiedinstructions; a program counter relative value calculating unit forcalculating, when a label which should be resolved by a difference inaddresses of two specified instructions has been detected, a programcounter relative value by subtracting an address of one of the twospecified instructions from an address of another of the two specifiedinstructions; a converting unit (1) for converting an instruction thathas a label that should be resolved by an address of a specifiedinstruction into an instruction with a size that is based on a size ofthe address of the specified instruction, (2) for converting aninstruction that has a label that should be resolved by a difference inaddresses of two specified instructions into an instruction with a sizethat is based on a size of the program counter relative value calculatedfrom the addresses of the two specified instructions; and an optimizedcode generating unit for generating optimized code by convertingaddresses of instructions in accordance with the sizes of instructionsafter conversion by the converting unit.

The above construction achieves an optimization apparatus for generatingprograms for a processor that executes branch instructions.

Here, the program counter relative value calculating unit may include alower bit subtracting unit and an upper bit subtracting unit, the lowerbit subtracting unit subtracting lower bits of the address of the one ofthe two specified instructions from lower bits of the address of theother of the two specified instructions, for setting a result of asubtraction as lower bits of the program counter relative value, andsending any carry generated in the subtraction to the upper bitsubtracting unit, and the upper bit subtracting unit subtracting upperbits of the address of one of the two specified instructions and anycarry received from the lower bit subtracting unit from upper bits ofthe address of the other of the two specified instructions, and forsetting a result of a subtraction as upper bits of the program counterrelative value.

The above construction achieves an optimization apparatus for generatingprograms for a processor which, when executing a branch instruction,calculates the address of a branch destination instruction using a carrymethod.

Here, the program counter relative value calculating unit may include alower bit subtracting unit and an upper bit subtracting unit, the lowerbit subtracting unit subtracting lower bits of the address of one of thetwo specified instructions from lower bits of the address of the otherof the two specified instructions without generating a carry and settinga result of a subtraction as lower bits of the program counter relativevalue, and the upper bit subtracting unit subtracting upper bits of theaddress of one of the two specified instructions from upper bits of theaddress of the other of the two specified instructions, and for settinga result of a subtraction as upper bits of the program counter relativevalue.

The above construction achieves an optimization apparatus for generatingprograms for a processor which, when executing a branch instruction,calculates the address of a branch destination instruction without usinga carry.

Here, the program counter relative value calculating unit may subtractupper bits of an address of one of the two specified instructions fromupper bits of an address of the other of the two specified instructions,set a result of a subtraction as upper bits of the program counterrelative value, and set lower bits of the other of the two specifiedinstructions as lower bits of the program counter relative value.

The above construction achieves an optimization apparatus for generatingprograms for a processor which, when executing a branch instruction,calculates the address of a branch destination instruction using anabsolute value.

The stated primary object can also be achieved by an assembler thatgenerates relocatable code from an instruction sequence, each address ofan instruction in the instruction sequence having upper bits thatindicate a memory address at which a processing packet is stored andlower bits that indicate a position of processing target instructionthat is included in the processing packet, the assembler including: alabel detecting unit for detecting a label in the instruction sequencethat should be resolved by a difference in addresses between twospecified instructions, and obtaining the addresses of the two specifiedinstructions; a program counter relative value calculating unit forcalculating a program counter relative value by subtracting an addressof one of the two specified instructions from an address of another ofthe two specified instructions; and a replacing unit for replacing thelabel with the program counter relative value calculated by the programcounter relative value calculating unit.

The above construction achieves an assembler for generating programs fora processor that executes branch instructions.

Here, the program counter relative value calculating unit may include alower bit subtracting unit and an upper bit subtracting unit, the lowerbit subtracting unit subtracting lower bits of the address of the one ofthe two specified instructions from lower bits of the address of theother of the two specified instructions, for setting a result of asubtraction as lower bits of the program counter relative value, andsending any carry generated in the subtraction to the upper bitsubtracting unit, and the upper bit subtracting unit subtracting upperbits of the address of one of the two specified instructions and anycarry received from the lower bit subtracting unit from upper bits ofthe address of the other of the two specified instructions, and forsetting a result of a subtraction as upper bits of the program counterrelative value.

The above construction achieves an assembler for generating programs fora processor which, when executing a branch instruction, calculates theaddress of a branch destination instruction using a carry method.

Here, the program counter relative value calculating unit may include alower bit subtracting unit and an upper bit subtracting unit, the lowerbit subtracting unit subtracting lower bits of the address of one of thetwo specified instructions from lower bits of the address of the otherof the two specified instructions without generating a carry and settinga result of a subtraction as lower bits of the program counter relativevalue, and the upper bit subtracting unit subtracting upper bits of theaddress of one of the two specified instructions from upper bits of theaddress of the other of the two specified instructions, and for settinga result of a subtraction as upper bits of the program counter relativevalue.

The above construction achieves an assembler for generating programs fora processor which, when executing a branch instruction, calculates theaddress of a branch destination instruction without using a carry.

Here, the program counter relative value calculating unit may subtractupper bits of an address of one of the two specified instructions fromupper bits of an address of the other of the two specified instructions,set a result of a subtraction as upper bits of the program counterrelative value, and set lower bits of the other of the two specifiedinstructions as lower bits of the program counter relative value.

The above construction achieves an optimization apparatus for generatingprograms for a processor which, when executing a branch instruction,calculates the address of a branch destination instruction using anabsolute value.

The stated primary object can also be achieved by a linker thatgenerates object code by combining relocatable code, each address of aninstruction in the relocatable code having upper bits that indicate amemory address at which a processing packet is stored and lower bitsthat indicate a position of processing target instruction that isincluded in the processing packet, the linker including: a relocationinformation detecting unit for detecting a label in the relocatable codethat should be resolved by a difference in addresses between twospecified instructions, and obtaining the addresses of the two specifiedinstructions; a program counter relative value calculating unit forcalculating a program counter relative value by subtracting an addressof one of the two specified instructions from an address of another ofthe two specified instructions; and a replacing unit for replacing thelabel with the program counter relative value calculated by the programcounter relative value calculating unit.

The above construction achieves a linker for generating programs for aprocessor that executes branch instructions.

Here, the program counter relative value calculating unit may include alower bit subtracting unit and an upper bit subtracting unit, the lowerbit subtracting unit subtracting lower bits of the address of the one ofthe two specified instructions from lower bits of the address of theother of the two specified instructions, for setting a result of asubtraction as lower bits of the program counter relative value, andsending any carry generated in the subtraction to the upper bitsubtracting unit, and the upper bit subtracting unit subtracting upperbits of the address of one of the two specified instructions and anycarry received from the lower bit subtracting unit from upper bits ofthe address of the other of the two specified instructions, and forsetting a result of a subtraction as upper bits of the program counterrelative value.

The above construction achieves a linker for generating programs for aprocessor which, when executing a branch instruction, calculates theaddress of a branch destination instruction using a carry method.

Here, the program counter relative value calculating unit may include alower bit subtracting unit and an upper bit subtracting unit, the lowerbit subtracting unit subtracting lower bits of the address of one of thetwo specified instructions from lower bits of the address of the otherof the two specified instructions without generating a carry and settinga result of a subtraction as lower bits of the program counter relativevalue, and the upper bit subtracting unit subtracting upper bits of theaddress of one of the two specified instructions from upper bits of theaddress of the other of the two specified instructions, and for settinga result of a subtraction as upper bits of the program counter relativevalue.

The above construction achieves a linker for generating programs for aprocessor which, when executing a branch instruction, calculates theaddress of a branch destination instruction without using a carry.

Here, the program counter relative value calculating unit may subtractupper bits of an address of one of the two specified instructions fromupper bits of an address of the other of the two specified instructions,set a result of a subtraction as upper bits of the program counterrelative value, and set lower bits of the other of the two specifiedinstructions as lower bits of the program counter relative value.

The above construction achieves a linker for generating programs for aprocessor which, when executing a branch instruction, calculates theaddress of a branch destination instruction using an absolute value.

The stated primary object can also be achieved by a disassembler thatreceives an indication of an address of an instruction in object codeand outputs an assembler name of the instruction at the indicatedaddress, each address of an instruction in the object code having upperbits that indicate a memory address at which a processing packet isstored and lower bits that indicate a position of processing targetinstruction that is included in the processing packet, the disassemblerincluding: a program counter relative value extracting unit forextracting, when the indicated instruction includes a program counterrelative value, the program counter relative value from the indicatedinstruction; a label addressing calculating unit for adding an addressof the indicated instruction to the extracted program counter relativevalue and setting an addition result as a label address; a storing unitfor storing a label name corresponding to each label address; and asearching unit for searching the storing unit for a label name thatcorresponds to the calculated label address and outputting thecorresponding label name.

The stated construction can disassemble a program that includes a branchinstruction. When the disassembled instruction is a branch instruction,the address of the branch destination instruction can be calculated fromthe program counter relative value. This address is then used to searchthe label table and so obtain the label name. As a result, the branchdestination can be displayed to the user in the readily understandableform of a label name, even when program counter relative values are usedin branch instructions.

Here, the label address calculating unit may include a lower bitcalculating unit and an upper bit calculating unit, the lower bitcalculating unit for adding lower bits of the address of the indicatedinstruction and lower bits of the program counter relative value,setting a result of an addition as lower bits of a label address, andsending any carry generated by the addition to the upper bit calculatingunit, and the upper bit calculating unit adding upper bits of theaddress of the indicated instruction, upper bits of the program counterrelative value, and any carry received from the lower bit calculatingunit, and setting a result of the an addition as upper bits of the labeladdress.

The above construction achieves a disassembler that can disassembleprograms for a processor which, when executing a branch instruction,calculates an address of a branch destination instruction using a carry.

Here, the label address calculating unit may include a lower bitcalculating unit and an upper bit calculating unit, the lower bitcalculating -unit adding lower bits of the address of the indicatedinstruction and lower bits of the program counter relative value withoutgenerating a carry, and setting a result of an addition as lower bits ofa label address, and the upper bit calculating unit adding upper bits ofthe address of the indicated instruction and upper bits of the programcounter relative value, and setting a result of an addition as upperbits of the label address.

The above construction achieves a disassembler that can disassembleprograms for a processor which, when executing a branch instruction,calculates an address of a branch destination instruction without usinga carry.

Here, the label address calculating unit may add upper bits of theaddress of the indicated instruction and upper bits of the programcounter relative value, set a result of an addition as upper bits of thelabel address, and set lower bits of the program counter relative valueas lower bits of the label address.

The above construction achieves a disassembler that can disassembleprograms for a processor which, when executing a branch instruction,calculates an address of a branch destination instruction using anabsolute value.

The stated primary object can also be achieved by a debugger thatreceives an indication of an address of an instruction in object codeand replaces the instruction at the indicated address with a replacementinstruction, each address of an instruction in the object code havingupper bits that indicate a memory address at which a processing packetis stored and lower bits that indicate a position of processing targetinstruction that is included in the processing packet, the debuggerincluding: a processing packet reading unit for reading a processingpacket that is indicated by upper bits of the indicated address from thememory and writing the processing packet into an instruction buffer; aninstruction writing unit for writing the replacement instruction intothe processing packet in the instruction buffer over an instruction thatis indicated by the lower bits of the indicated address; and aprocessing packet writing unit for writing the processing packet in theinstruction buffer back into the memory after the replacementinstruction has been written.

The above construction reads instructions in units of processing packetsfrom a memory that stores instructions in one-byte storage packets,rewrites instructions in an instruction buffer, and writes instructionsback into the memory in units of processing packets. This achieves adebugger that can debug instructions whose length is not an integernumber of bytes.

The stated primary object can also be achieved by a compiler thatgenerates an instruction sequence from source code, the compilergenerating a program counter relative value calculating instruction thatis executed by a processor, the program counter relative valuecalculating instruction being an instruction that performs a calculationusing a first value and a program counter relative value and uses aresult of the calculation to update the first value, the first valuebeing one of (a) a value of a program counter stored in a register, and(b) the value stored in a program counter of the processor, whereinupper bits of the first value indicate a memory address at which aprocessing packet is stored, and lower bits of the first value of theprogram counter indicate a processing target instruction that isincluded in the processing packet.

The above construction achieves a compiler that generates programs for aprocessor that executes program counter relative value calculatinginstructions.

Here, the processor may include a lower bit calculating unit and anupper bit calculating unit, the program counter relative valuecalculating instruction having the lower bit calculating unit perform alower bit calculation and the upper bit calculating unit perform anupper bit calculation, the lower bit calculation being an addition usinglower bits of the first value and lower bits of the value of the programcounter relative value, where a result of the lower bit calculation isset as the lower bits of the first value and any generated carry is sentto the upper bit calculating unit, and the upper bit calculation beingan addition using upper bits of the first value, upper bits of the valueof the program counter relative value and any carry received from thelower bit calculating unit, where a result of the upper bit calculationis set as the upper bits of the first value.

The above construction achieves a compiler that generates a program fora processor which, when executing a program counter relative valuecalculating instruction, performs a calculation using a value of theprogram counter and the program counter relative value according to acarry method.

Here, the processor may include a lower bit calculating unit and anupper bit calculating unit, the program counter relative valuecalculating instruction having the lower bit calculating unit perform alower bit calculation and the upper bit calculating unit perform anupper bit calculation, the lower bit calculation being an addition usinglower bits of the first value and lower bits of the value of the programcounter relative value that does not generate a carry, where a result ofthe lower bit calculation is set as the lower bits of the first value,and the upper bit calculation being a calculation using upper bits ofthe first value and upper bits of the value of the program counterrelative value, where a result of the upper bit calculation is set asthe upper bits of the first value.

The above construction achieves a compiler that generates a program fora processor which, when executing a program counter relative valuecalculating instruction, performs a calculation using a value of theprogram counter and the program counter relative value withoutgenerating a carry.

Here, the processor may includes an upper bit calculating unit, theprogram counter relative value calculating instruction having the upperbit calculating unit perform an upper bit calculation and setting lowerbits of the program counter relative value as lower bits of the firstvalue, and the upper bit calculation being an addition using upper bitsof the first value and upper bits of the value of the program counterrelative value, where a result of the upper bit calculation is set asthe upper bits of the first value.

The above construction achieves a compiler that generates a program fora processor which, when executing a program counter relative valuecalculating instruction, performs a calculation using a value of theprogram counter and the program counter relative value according to anabsolute value calculating method.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings-which illustrate a specificembodiment of the invention. In the drawings:

FIG. 1 is a block diagram showing the construction of a conventionalprocessor;

FIG. 2A shows the format of one instruction executed by the processor ofthe first embodiment of the present invention;

FIG. 2B shows the format of another instruction executed by theprocessor of the first embodiment of the present invention;

FIG. 2C shows the format of another instruction executed by theprocessor of the first embodiment of the present invention;

FIG. 2D shows the format of another instruction executed by theprocessor of the first embodiment of the present invention;

FIG. 2E shows the format of another instruction executed by theprocessor of the first embodiment of the present invention;

FIG. 3A shows an instruction packet that is the unit used for storingand reading instructions in this first embodiment;

FIG. 3B shows the read order of instructions;

FIG. 3C shows the execution order of instructions;

FIG. 4 shows an example of the methods used by a conventional processorto store and read instructions that are not byte-aligned;

FIG. 5 shows the procedure by which the object code to be executed bythe processor is generated by a compiler, optimization apparatus,assembler, and linker;

FIG. 6 is a block diagram showing the details of the processor 309 andthe external memory;

FIG. 7 is an increment table showing the rules used to increment thein-packet address;

FIG. 8A is an addition table showing the addition rules used when addingthe lower 3 bits of the address of a branch instruction to lower 3 bitsof the PC relative value;

FIG. 8B is a subtraction table showing the subtraction rules used whensubtracting the lower 3 bits of the PC relative value from the lower 3bits of a branch destination address;

FIG. 9 is a block diagram showing the components and input/output dataof the optimization apparatus 303;

FIG. 10 is a flowchart showing the operation procedure of theoptimization apparatus;

FIG. 11 shows part of the optimization processing code 903 generated bythe code optimization apparatus 902;

FIG. 12 shows the address assigned codes 916 generated from theoptimization processing code 903 shown in FIG. 11;

FIG. 13 shows the label information 906 generated from the addressassigned codes 916 shown in FIG. 12;

FIG. 14 shows the optimized code 304 generated from the address assignedcodes 916 shown in FIG. 12;

FIG. 15 is a block diagram that shows the construction of the assembler305 shown in FIG. 5 and the input/output data related to the assembler305;

FIG. 16 is a flowchart showing the operation of the assembler;

FIG. 17 shows the machine language codes 803 that are generated from theoptimized code 304 shown in FIG. 14;

FIG. 18 shows the label information that is generated from the machinelanguage codes shown in FIG. 17;

FIG. 19 shows the relocatable codes that are generated from the machinelanguage codes 803 shown in FIG. 17;

FIG. 20 is a block diagram showing the construction of the linker 307and the I/O (input/output) data of the linker 307;

FIG. 21 is a flowchart showing the operation of the linker 307;

FIG. 22 shows the relocatable codes;

FIG. 23 shows the state when the relocatable codes 814 shown in FIG. 19have been combined with the relocatable code shown in FIG. 22;

FIG. 24 shows the resulting combined codes 703;

FIG. 25 shows the label information that is generated from the combinedcodes 703 shown in FIG. 24;

FIG. 26 shows the object codes generated from the combined codes 703shown in FIG. 24;

FIG. 27 shows the object code generated by the second embodiment of thepresent invention;

FIG. 28A shows the construction of an instruction packet in the thirdembodiment;

FIG. 28B shows the types of instructions used in the third embodiment;

FIG. 28C shows the relation between in-packet addresses and theinstruction units in a packet;

FIG. 29A is an addition table showing the addition rules for adding thelower 3 bits of the address of the branch instruction and the lower 3bits of the PC relative value in the calculation method of the fourthembodiment that does not use a carry;

FIG. 29B is a subtraction table showing the subtraction rules forsubtracting the lower 3 bits of the address of the branch instructionfrom the lower 3 bits of the address of the branch destinationinstruction in the calculation method of the fourth embodiment that doesnot use a carry;

FIG. 30 shows the object code that is generated by the addresscalculation method of the fourth embodiment that does not use a carry;

FIG. 31A is an addition table showing the addition rules for adding thelower 3 bits of the address of the branch instruction and the lower 3bits of the PC relative value in the calculation method of the fifthembodiment that uses absolute values;

FIG. 31B is a subtraction table showing the subtraction rules forsubtracting the lower 3 bits of the address of the branch instructionfrom the lower 3 bits of the address of the branch destinationinstruction in the calculation method of the fifth embodiment that usesabsolute values;

FIG. 32 shows the object code that is generated by the above addresscalculation method of the fifth embodiment that uses absolute values;

FIG. 33 shows the object code that has been generated using the linearcalculation method of the sixth embodiment;

FIG. 34 shows the processor of the seventh embodiment;

FIG. 35A shows the operation that corresponds to a PC adding instructionwhich is shown in mnemonic form;

FIG. 35B shows the operation that corresponds to a PC subtractinginstruction which is shown in mnemonic form;

FIG. 36 shows the construction of the compiler of the eighth embodimentof the present invention;

FIG. 37 is a flowchart showing the operation of the compiler;

FIG. 38 shows source code which is written in C language;

FIG. 39 shows the intermediate codes that have been generated from thesource program shown in FIG. 38;

FIG. 40 shows the assembler code that has been produced by convertingthe intermediate codes shown in FIG. 39;

FIG. 41 is a block diagram showing the construction of the debugger anddisassembler of the present embodiment;

FIG. 42 is a flowchart showing the operating procedure of a disassemblerof the present invention; and

FIG. 43 is a flowchart showing the operation of the debugger of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of several embodiments of thepresent invention, with reference to the accompanying drawings.

First Embodiment

This first embodiment relates to an optimization apparatus, anassembler, and a linker that generate programs where read operations andexecute operations have different units, and to a processor forexecuting such programs.

Formats of the Instructions Executed by the Processor

The following explains the formats of the instructions executed by theprocessor of this first embodiment. These formats are shown in FIGS.2A-2E. The instructions executed by the present processor areconstructed so that 21 bits is set as one instruction unit. For thepresent processor, there are both one-unit (i.e., 21-bit) and two-unit(i.e., 42-bit) instructions.

The format information 101 is written as one bit and shows the length ofeach instruction. When the format information 101 is “0”, this showsthat the unit including this format information 101 forms one completeinstruction, which is to say, a 21-bit instruction. When the formatinformation 101 is “1”, this shows that the unit including this formatinformation 101 and the following unit together form one two-unitinstruction, which is to say, a 42-bit instruction.

The parallel execution boundary information 100 is also written as onebit and shows whether a parallel execution boundary exists between theinstruction formed by the present unit and the following instruction.When the parallel execution boundary information 100 is “1”, this showsthat a parallel execution boundary exists between the instructionincluding this parallel execution boundary information 100 and thefollowing instruction, so that these instructions will be executed indifferent cycles. When the parallel execution boundary information 100is “0”, this shows that no parallel execution boundary exists betweenthe instruction including this parallel execution boundary information100 and the following instruction, so that these instructions will beexecuted the same cycle.

The remaining bits in each instruction are used to show an operation.This means that 19 bits can be used to indicate the operation in a21-bit instruction and that 40 bits can be used to indicate theoperation in a 42-bit instruction. The fields marked “Op1”, “Op2”,“Op3”, and “Op4” are used to store opcodes that indicate the type ofoperation to be performed. The field marked “Rs” is used to store theregister number of a register used as the source operand and the fieldmarked “Rd” is used to store the register number of a register used asthe destination operand. The fields marked “imm5” and “imm32” arerespectively used to store 5-bit and 32-bit immediates that are used incalculations. Finally, the fields marked “disp13” and “disp32” arerespectively used to store 13-bit and 32-bit displacements.

Transfer instructions and arithmetic instructions that handle long (suchas 32-bit) constants and branch instructions that use largedisplacements are defined as 42-bit instructions. Most otherinstructions are defined as 21-bit instructions. Of the two units usedto compose a 42-bit instruction, the latter unit is only used to storepart of the long constant or displacement, and so does not store theopcode of the instruction.

Reading and Execution of Instructions by the Processor

The following explains the operation of the present processor whenreading and executing instructions. Note that the processor of thepresent embodiment has a premise that static parallel scheduling isused. FIG. 3A shows an instruction packet that is the unit used forstoring and reading instructions. Each instruction packet is composed ofthree instruction units (63 bits) and dummy data (1 bit). In each cycle,the processor reads instructions using this fixed 64-bit packet length.Packets of this size are used because the 21-bit unit size ofinstruction is not suited to reading from memory. Accordingly, a numberof such instructions are read together with dummy data to make the totalpacket size equal to an integer number of bytes. In this example, sincethe number of instruction units in each instruction packet is not apower of two, there is the following special effect. This effectovercomes the problems that occur when positions of the units insideinstruction packets are expressed using binary. In the followingexplanation, the three units in an instruction packet are called thefirst, second and third units in order starting from the unit with thelowest address value.

FIG. 3B shows the read order of instructions. As shown in the figure,one instruction packet is read in each cycle.

FIG. 3C shows the execution order of instructions. In each cycle,instructions are executed as far as the next parallel executionboundary. This means that the instructions are executed up to andincluding an instruction whose parallel execution boundary information100 is “1”. Instruction units that are read but not executed areaccumulated in the instruction buffer, and are executed in a latercycle.

As described above, the processor of the present embodiments readsinstructions using packets of a fixed length, but only executes asuitable number of units in each cycle depending on parallelism of theinstructions. The reason that the present processor can start theexecution of instructions in one cycle at any of the instruction unitsin an instruction packet is that an in-packet address specifies aninstruction unit in an instruction packet. This is described in moredetail later.

FIG. 4 shows an example of the methods used by a conventional processorto store and read instructions that are not byte-aligned. When 21-bitinstructions that are not byte-aligned are to be read in byte-units,three unused bits have to be added to the end of each instruction tomake the instruction length 24-bits. This means that what areessentially 21-bit instructions are stored into and read from memory in24-bit units. The length of three of such instructions is 72 bits, sothat the storage of three instructions in a 64-bit packet in the presentembodiment reduces overall program size.

Note that while the present embodiment describes the packet constructionwhen 21-bit instructions are used, the invention is not limited to thisinstruction length. It is equally possible to construct instructionpackets of instructions of a different length and to read theinstructions using such instruction packets. As one example, wheninstructions are n-bits long, values of m and r may be selected so as togive a maximum value of n*m÷(n*m+r) subject to (n*m+r)mod8=0. One packetis then composed of m instruction units (each being n bits long) andr-bit dummy data. By doing so, instruction packets can be composed ofmultiple-byte size using relatively little dummy data.

Method for Expressing Instruction Addresses

The following explains the method used to express instruction addressesin the present embodiment. Here, an instruction address refers to theaddress used to specify the position of a unit and is expressed as 32bits.

The upper 29-bits of a 32-bit address are used to specify an instructionpacket and so are called the “packet address”. This packet address isexpressed as a 29-bit hexadecimal figure in a format such as“29′h01234567”. A value produced by shifting the value of this packetaddress by 3-bits to the left is the memory address at which theinstruction packet is stored.

The lower 3-bits in a 32-bit address are used to specify an instructionunit included in the instruction packet and so are called the “in-packetaddress”. This in-packet address is expressed as a 3-bit binary value ina format such as “3′b001”. As examples, the in-packet address “3′b001”specifies the first unit in an instruction packet, the in-packet address“3′b010” specifies the second unit, and the in-packet address “3′b100”specifies the third unit. However, the in-packet addresses are notlimited to these specific values. Other values may be used provided thatthe instruction units in an instruction packet are each specified usingtheir own value.

The indicating of addresses in this embodiment is such that only 3 bitsare assigned for eight-bytes of instructions. This gives the sameresults as when a conventional processor assigns a separate address toeach byte, since the upper 29-bits of addresses assigned to eight-bytesof instructions will be the same.

Method for Generating the Object Code Executed by the Processor

The following explains the method for generating the object code that isexecuted by the processor of the present embodiment.

First, the terminology to be used in this explanation is defined.

A “PC relative value” is the difference between the addresses of twoinstructions.

A “label” is either an “instruction address-resolved label” or a “PCrelative value-resolved label”. Absolute address-resolved labels arereplaced with absolute addresses of instructions during the processingthat converts a program into object code. An example of such a label isthe label “L2” in the transfer instruction “mov L2,r1” that transfers aninstruction stored in memory to the register r1. PC relativevalue-resolved labels are replaced with PC relative values during theprocessing that converts a program into object code. An example of sucha label is the label “L1” in the unconditional branch instruction “braL1” that performs an unconditional branch using the PC relative value.“Local labels” and “external labels” also exist as other types of label.When a label and the instruction including the label are included in thesame module (a module being a subprogram composed of an instructionsequence achieving one processing function), such label is called alocal label, while when the label and instruction including the labelare included in different modules, such label is called an externallabel.

FIG. 5 shows the procedure by which the object code to be executed bythe processor is generated by a compiler, optimization apparatus,assembler, and linker. An overview of the functions of these componentsis given below.

The compiler 301 analyzes the content of the source code 300 that iswritten in a high-level language like C and outputs assembler code 302.

The optimization apparatus 303 assigns temporary addresses to theassembler code 302, links the instruction sequences in groups of threeinstruction units, and outputs optimized code 304 as the linked results.In this process, local labels are calculated as PC relative values orinstruction addresses. The instruction size, which is to say, whether aninstruction should be expressed as a one-unit instruction or as atwo-unit instruction, is then determined based on the value of the PCrelative value or the instruction address.

The assembler 305 outputs relocatable codes 306 which it generates fromthe optimized code 304. This processing converts local labels thatshould be resolved with PC relative values into PC relative values.

The linker 307 combines a plurality of modules. That is, the linker 307combines a plurality of relocatable codes 306 and outputs the resultingobject code 308. In this processing, unresolved labels are convertedinto PC relative values or instruction addresses.

The processor 309 executes the object code 308.

As described above, a program written in a high-level language isconverted by the compiler 301, the optimization apparatus 303, theassembler 305, and the linker 307 into object code that is in a formatexecutable by the processor. Each label in the program is converted intoa PC relative value or an instruction address by one of the steps in theabove procedure. Address resolution for local labels that should beresolved by a PC relative value is performed by the assembler 305.Address resolution for local labels that should be resolved by aninstruction address and address resolution for external labels areperformed by the linker 307.

The following describes the construction and operation of the processor309, the linker 307, the assembler 305, and the optimization apparatus303 shown in FIG. 4.

Processor

FIG. 6 is a block diagram showing the details of the processor 309 andthe external memory.

The processor 309 is capable of executing a maximum of threeinstructions in parallel. This processor 309 includes calculators 401a˜401 c, general registers 402, an upper PC 403, a lower PC 404, anupper PC calculator 411, a lower PC calculator 405, an INC 412, aninstruction buffer 408, an prefetch upper counter 410, a prefetch lowercounter 413, instruction decoder 409 a˜409 c, a PC relative valueselector 420, an immediate selector 421, an operand data buffer 423, andan operand address buffer 422. The external memory includes the datamemory 406 and the instruction memory 407.

In the following explanation, the upper PC 403 and the lower PC 404 willbe collectively referred to as the “PC”, and the upper PC calculator 411and the lower PC calculator 405 will be collectively referred to as the“PC calculator”.

The first calculator 401 a, the second calculator 401 b, and the thirdcalculator 401 c each perform one calculation. These calculators arecapable of calculating at the same time.

The general registers 402 store data, addresses and other data.

The upper PC 403 stores the upper 29 bits of the address of the firstinstruction in a set of instructions to be executed in the next cycle,which is to say, a packet address.

The lower PC 404 stores the lower 3 bits of the address of the firstinstruction in a set of instructions to be executed in the next cycle,which is to say, an in-packet address.

The instruction memory 407 stores instructions that are expressed by theobject code 308.

The instruction buffer 408 stores instructions that have been read fromthe instruction memory 407.

The first instruction decoder 409 a, the second instruction decoder 409b, and third instruction decoder 409 c decode instructions and, if therespective instructions are executable, give indications to othercomponents in the processor to have the instructions executed. The firstinstruction decoder 409 a receives an input of the first instructionstored in the instruction buffer 408, the second instruction decoder 409b an input of the next instruction, and the third instruction decoder409 c an input of a next instruction. These instruction decoders 409a˜409 c investigate whether there is a parallel execution boundarybetween the instruction units and only have the instructions that shouldbe executed in the present cycle executed. As one example, when aninstruction performs a calculation using a constant, the constant issent to the first calculator 401 a via the immediate selector 421 andthe first calculator 401 a is instructed to perform the calculation. Fora branch instruction, a PC relative value is sent via the PC relativevalue selector 420 to the lower PC calculator 405 and upper PCcalculator 411 that are then instructed to update the PC. Theinstruction decoders 409 a˜409 c send control signals showing the numberof executed instruction units to have the INC 412 update the PCincrement, and send control signals showing the number of executedinstruction units to the instruction buffer 408 to have the executedinstruction units deleted from the instruction buffer 408.

The PC relative value selector 420 outputs the PC relative valueoutputted by the instruction decoders 409 a 409 c to the lower PCcalculator 405 and the upper PC calculator 411.

The immediate selector 421 outputs an immediate outputted by theinstruction decoders 409 a˜409 c to the general registers 402 and thecalculators 401 a˜401 c.

The INC 412 receives information regarding the number of executedinstruction units via control signals sent by the instruction decoders409 a˜409 c, and increments the value of the upper PC 403 and the lowerPC 404 in accordance with this number. By doing so, the INC 412 sets thepacket address of the first instruction in the set of instructions to beexecuted in the next cycle in the upper PC 403 and the in-packet addressof the first instruction in the set of instructions to be executed inthe next cycle in the lower PC 404.

The upper PC calculator 411 and lower PC calculator 405 respectivelyupdate the upper PC 403 and the lower PC 404. When a branch instructionis decoded by the instruction decoders 409 a˜409 c, the upper PCcalculator 411 and lower PC calculator 405 respectively receive theupper 29 bits and the lower 3 bits of the PC relative value included inthe branch instruction of the PC relative value. The lower PC calculator405 increases or decreases the present value of the lower PC 404 by thelower 3 bits in the PC relative value and sends the calculation resultto the lower PC 404 as the new lower PC. The upper PC calculator 411increases or decreases the present value of the upper PC 403 by theupper 29 bits in the PC relative value and sends the calculation resultto the upper PC 403 as the new upper PC. This operation of the PCcalculators is described later in this specification. As describedabove, when a branch instruction is executed, the packet address of thebranch destination instruction that is to be executed next is set in theupper PC 403 and the in-packet address is set in the lower PC 404. Thereare also cases where the upper PC calculator 411 and lower PC calculator405 update the PC by calculating an address using a PC relative valueand an address stored in the general registers 402.

The prefetch upper counter 410 shows the upper 29 bits of the address ofthe first instruction in the set of instructions to be read from theinstruction memory 407, which is to say, the packet address. Theprefetch upper counter 410 normally increments this value by one in eachcycle. When a branch instruction was executed in the previous cycle, thepacket address of the branch destination instruction set in the upper PC403 is sent to the prefetch upper counter 410 where it is set in placeof the present value in the prefetch upper counter 410.

The prefetch lower counter 413 shows the lower 3 bits of the address ofthe first instruction in the set of instructions read from theinstruction memory 407, which is to say, the in-packet address. In thisembodiment, the value “3′b000” is set in the prefetch lower counter 413.As a result, the instructions to be read are indicated in packet units,so that one packet is sent from the instruction memory 407 to theinstruction buffer 408 in each cycle.

The data memory 406 stores operand data.

The operand data buffer 423 and operand address buffer 422 are buffersthat are located between the data memory 406 and the processor.

The following explains the incrementing method and calculating methodfor instruction addresses. This is the most characteristic feature ofthe present embodiment.

Incrementing Method for Instruction Addresses

The incrementing of addresses is performed by adding an increment valueto the in-packet address of an instruction, and adding any carryproduced by the addition to the packet address.

FIG. 7 is an increment table showing the rules used to increment thein-packet address. As shown in the figure, when the in-packet address is“3′b000” or “3+b010”, the incrementing of the instruction address isperformed by adding 2 to the in-packet address. When the in-packetaddress is “3′b100”, a carry to the packet address is produced (which isto say, 1 is to be added to the upper 29 bits of the instructionaddress) and the in-packet address is updated to “3′b000”. This meansthat the incrementing of the in-packet address is a calculation thatcycles through the three values “3′b000”, “3′b010”, and “3+b100”. As oneexample, when the increment value is “2” and the value of the in-packetaddress before incrementing is “3′b100”, the packet address afterincrementing is “3+b010” and a carry of “1” to the packet address isgenerated.

Note that in the present embodiment, the in-packet address does not needto be expressed in binary. This is especially effective when the numberof instruction units in an instruction packet is not a power of 2. Whenthis is the case, it is not possible to express the position of aninstruction unit in an instruction packet in binary and use a binarycalculation to shift the position of an instruction unit. However, inthe present embodiment, the position of an instruction unit in aninstruction packet is expressed using m different values. By using acalculation that cycles through these m values, the specifying ofinstruction units and the calculations for shifting the instructionposition can be achieved even if the number of instruction units in aninstruction packet is not a power of 2.

Method for Calculating the Instruction Address

The following explains the carry method which is one of the methods usedfor calculating the instruction addresses in the present invention.Other methods used to calculate addresses are a separation method, anabsolute position indicating method, and a linear addressing method,though these will be described later in this specification. In the carrymethod, the upper 29 bits and lower 3 bits of an instruction address arecalculated separately. However, when calculating the upper bits, anycarry to or from the upper 29 bits that occurred when calculating thelower 3 bits is taken into account.

The following explains the method by which the present processor addsthe address of a branch instruction and a PC relative value to find abranch destination address. The lower PC calculator 405 shown in FIG. 6adds the lower 3 bits of the address of a branch instruction to thelower 3 bits of the PC relative value. FIG. 8A is an addition tableshowing the addition rules used when adding the lower 3 bits of theaddress of a branch instruction to lower 3 bits of the PC relativevalue. As shown in FIG. 8A, this addition of the lower 3-bit valuesdiffers from a binary calculation in being a calculation that cyclesthrough the three values “3′b000”, “3+b001”, and “3′b100”. When a carryoccurs as shown in FIG. 8A, the lower PC calculator 405 sends the carryto the upper PC value to the upper PC calculator 411.

The upper PC calculator 411 shown in FIG. 6 adds the upper 29 bits ofthe address of a branch instruction to the upper 29 bits of the PCrelative value. When doing so, if the calculation of the lower PCcalculator 405 has resulted in a carry to the upper PC, the upper PCcalculator 411 also adds this carry. This addition is a normal additionof binary values.

The addition results of the lower PC calculator 405 and upper PCcalculator 411 form the address of the branch destination instruction.The addition result for the lower 3 bits is set in the lower PC 404 andthe addition result for the upper 29 bits is set in the upper PC 403.

The following explains the calculations of the optimization apparatus303, assembler 305, and linker 307 for finding the PC relative value,which is to say the subtraction of the branch instruction address fromthe branch destination address. Like the addition described above, thissubtraction is performed separately for the upper 29 bits and lower 3bits. The lower address subtraction means 907 of the optimizationapparatus 303, the lower address subtraction means 806 of the assembler305, and the lower address subtraction means 706 of the linker 307subtract the lower 3 bits of the branch instruction address from thelower 3 bits of the branch destination address. FIG. 8B is a subtractiontable showing the subtraction rules used when subtracting the lower 3bits of the PC relative value from the lower 3 bits of a branchdestination address. As shown in FIG. 8B, this subtraction of the lower3-bit values differs from a binary calculation in being a calculationthat cycles through the three values “3′b000”, “3′b010”, and “3′b100”.When a carry occurs as shown in FIG. 8B, the lower address subtractionmeans that performs the calculation (such as lower address subtractionmeans 907) sends the carry from the upper PC value to the correspondingupper address subtraction means (such as upper address subtraction means910). The various upper address subtraction means are described in moredetail later.

The upper address subtraction means 910 in the optimization apparatus303, the upper address subtraction means 809 in the assembler 305, andupper address subtraction means 709 in the linker 307 subtract the upper29 bits of the address of a branch instruction from the upper 29 bits ofthe address of the branch destination instruction. When doing so, if thecalculation of the lower address subtraction means 907 (or similar) hasresulted in a carry from the upper PC, the upper address subtractionmeans 910 (or similar) also subtracts this carry. This subtraction is anormal subtraction of binary values.

These subtraction results respectively form the lower 3 bits and thehigher 29 bits of the PC relative value. This method is also used whenthe processor finds the address of a branch destination instruction byexecuting a subtraction on the address of a branch instruction and a PCrelative value.

The optimization apparatus 303, assembler 305, and linker 307, whichcalculate a PC relative value from the difference between the address ofa branch destination instruction and the address of a branchinstruction, and the processor 309, which calculates the address of abranch destination instruction using this PC relative value, calculateaddresses using the same carry method. As a result, when executing abranch instruction, the processor can correctly calculate the address ofa branch destination instruction from the PC relative value. Thisaddress calculation method that uses a carry has a feature in that itcan calculate addresses perform separate calculations for upper bits andlower bits while maintaining the continuity between the two.

Optimization Apparatus

FIG. 9 is a block diagram showing the components and input/output dataof the optimization apparatus 303 shown in FIG. 5. This optimizationapparatus 303 optimizes the assembler code 302 generated by the compiler301, links the instruction sequences together in packets of threeinstruction units, and outputs the resulting optimized code 304. Theoptimization apparatus 303 includes a code optimization apparatus 902,an address assigning means 904, a label detecting means 905, a loweraddress subtraction means 907, an upper address subtraction means 910,an address difference calculating means 912, and a label informationresolving means 914.

The code optimization apparatus 902 optimizes the assembler code 302 andso generates the optimization processing code 903. This processing ofthe code optimization apparatus 902 is the same as any well-knownoptimization apparatus, and so will not be described.

The address assigning means 904 estimates an address for eachinstruction in the optimization processing code 903 produced by the codeoptimization apparatus 902 and assigned an estimated address to eachinstruction. These addresses are called provisional addresses in thisspecification. As a result, the address assigning means 904 outputs theaddress assigned codes 916.

The label detecting means 905 detects local labels from the addressassigned codes 916. On detecting a label that should be resolved by aninstruction address, the label detecting means 905 obtains theprovisional address of the instruction including this label. Conversely,on detecting a label that should be resolved by a PC relative value, thelabel detecting means 905 obtains the provisional addresses of theinstruction including this label and the branch destination instruction.After this, the label detecting means 905 outputs the label information906 that shows the instructions that include labels and information onvalues for resolving these labels.

The lower address subtraction means 907, the upper address subtractionmeans 910, and the address difference calculating means 912 calculatethe PC relative values for labels, in the label information 906, thatshould be resolved by PC relative values.

The lower address subtraction means 907 subtracts the lower 3 bits ofthe provisional address of a branch instruction from the lower 3 bits ofthe provisional address of the branch destination instruction andoutputs the resulting carry value 908 and lower subtraction result 909.

The upper address subtraction means 910 subtracts the upper 29 bits ofthe provisional address of a branch instruction and the carry value 908calculated by the lower address subtraction means 907 from the upper 29bits of the provisional address of the branch destination instructionand outputs the resulting upper subtraction result 911.

The address difference calculating means 912 finds the addressdifference 913 by setting the lower subtraction result 909 calculated bythe lower address subtraction means 907 as the lower 3 bits and theupper subtraction result 911 calculated by the upper address subtractionmeans 910 as the upper 29 bits.

The label information resolving means 914 converts an instruction in theoptimization processing code 903 including the present label into aninstruction of a suitable size, based on an address that was estimatedand assigned by the address assigning means 904 or the addressdifference 913 found by the address difference calculating means 912. Ifthe assigned address or the address difference 913 can be expressedusing no more than 13 bits, the label information resolving means 914converts the instruction into a 21-bit instruction, or if not the labelinformation resolving means 914 converts the instruction into a 42-bitinstruction.

After the labels have been resolved, the label information resolvingmeans 914 links the instruction sequences into packets of threeinstruction units and outputs the result as the optimized code 304.

The following describes a specific operation of the optimizationapparatus 303.

FIG. 10 is a flowchart showing the operation procedure of theoptimization apparatus.

First, the code optimization apparatus 902 optimizes the assembler code302 and generates optimization processing code 903. Part of theoptimization processing code 903 generated by the code optimizationapparatus 902 is shown in FIG. 11. Of the instructions in FIG. 11,“L1:mov r2,r1” 1000 shows the position of the label L1 and is aninstruction that indicates a transfer from register r2 to register r1.The instruction “jsr f” is a function call that performs a relativebranch to the label f (an external label). A return from the functioncall to this address is performed by a “ret” instruction. Theinstruction “add r0,r4” adds the values of registers r0 and r4 andstores the result in register r4. The instruction “and r1,r3” 1003calculates a logical AND for the values in register r1 and r3 and storesthe result in register r3. The instruction “mov L2,r2” 1004 transfersthe address of the instruction located at the label L2 into the registerr2. The instruction “id (r2),r0” 1005 transfers the data stored at theaddress stored in register r2 into the register r0. The instruction “braL1” 1006 performs an indirect branch to the label L1 (a local label).Note that in FIG. 11, the instructions that continue after instruction1007 have been omitted, though these instructions do not include aninstruction located at the label f (step S9001).

The address assigning means 904 assigns a provisional address to eachinstruction in the optimization processing code 903 and so generatesaddress assigned codes 916. FIG. 12 shows the address assigned codes 916generated from the optimization processing code 903 shown in FIG. 11. Inthis example, provisional addresses starting from the value“32′b00000800” have been assigned (step S9002).

The label detecting means 905 detects local labels in the addressassigned codes 916 and outputs label information 906 composed ofinstructions that include the detected labels and information on thevalues used to resolve those labels. FIG. 13 shows the label information906 that is generated from the address assigned codes 916 shown in FIG.12. As shown in this figure, label L2 of instruction 1104 is detected asa label that should be resolved by an instruction address and label L1is detected as a label that should be resolved by a PC relative value.Information showing the address for resolving the label L2 is appendedto the instruction “mov L2,r2” that includes the label L2, andinformation showing the addresses of the branch destination instructionand branch instruction to be used for calculating a PC relative value isappended to the instruction “bra L1” that includes the label L1. Notethat since the label f in instruction 1101 is an external label, it isnot optimized (steps S9003, S9004).

When the label information 906 includes a label that should be resolvedby a PC relative value, processing to calculate this PC relative valueis performed. The lower address subtraction means 907 calculates thelower 3 bits of the value shown by the label L1 that is a PC relativevalue. The lower address subtraction means 907 subtracts the lower 3bits “3′b0101” of the provisional address “32′h00000812” of the branchinstruction 1106 from the lower 3 bits “3′b000” of the provisionaladdress “32′h00000800” of the branch destination instruction 1100. As aresult, “1” is obtained as the carry value 908, and “3′b100” is obtainedas the lower subtraction result 909 (steps S9005, S9006).

The upper address subtraction means 910 calculates the upper 29 bits ofthe value shown by the label L1 that is a PC relative value. The upperaddress subtraction means 910 subtracts the upper 29 bits “29′h00000102”of the provisional address of the branch instruction 1106 and the carryvalue 908 “1” generated by the lower address subtraction means 907 fromthe upper 29 bits “29′h00000100” of the provisional address of thebranch destination instruction 1100. As a result, “29′h1ffffffd” (“−3”in base 10, minus numbers being hereafter shown using a complement) isobtained as the upper subtraction result 911 (step S9007).

The address difference calculating means 912 finds the addressdifference, which is to say the PC relative value, by setting the lowersubtraction result 909 as the lower bits and the upper subtractionresult 911 as the upper bits. In this example, the address differencecalculating means 912 sets “3′b100” as the lower bits and “29′h1ffffffd”as the upper bits, giving an address difference of “32′hffffffec” (stepS9008).

The label information resolving means 914 judges whether the value usedto resolve the label in the label information 906 can be expressed by a13-bit value. The value that resolves the label L2 shown in FIG. 13 is“32′h12345678”, so that this value cannot be expressed as a 13-bitvalue, meaning that instruction 1104 including this label L2 will becomea 42-bit instruction. On the other hand, the value used to resolve labelL1 is “32′hffffffec”, which can be expressed by a 13-bit value.Accordingly, the instruction 1106 that includes label L1 will become a21-bit instruction (steps S9009, S9010, S9011).

The label information resolving means 914 links the instructionsequences into packets of three instruction units, based on the addressassigned codes 916. When doing so, the label information resolving means914 converts instructions that include labels into instructions of thedetermined size. Here, one instruction unit is used for 21-bitinstructions, and two units are used for 42-bit instructions. Afterthis, the label information resolving means 914 outputs the instructionsequences that it has converted into packets as the optimized code 304.FIG. 14 shows the optimized code 304 generated from the address assignedcodes 916 shown in FIG. 12. In FIG. 14, each row shows the instructionsthat form one instruction packet, with the marks “∥” showing theboundaries between instructions in a packet. Curved brackets “( )” areused in this drawing to indicate 42-bit instructions that each occupytwo units (step S9012).

As described above, addresses are estimated with a calculation methodthat uses a carry. In this way, a suitable optimization apparatus for aprocessor that uses a carry method can be achieved.

Note that the provisional addresses assigned by the address assigningmeans 904 and the PC relative values calculated by the addressdifference calculating means 912 are values that are estimated fordetermining the sizes of all instructions that include labels. There arecases when these estimates differ from the actual values, so that thesevalues are not used hereafter in the processing.

Assembler

FIG. 15 is a block diagram that shows the construction of the assembler305 shown in FIG. 5 and the input/output data related to the assembler305. This assembler 305 converts the optimized code 304 generated by theoptimization apparatus 303 into relocatable codes 306 that have arelocatable address format. The assembler 305 includes a machinelanguage code generating means 802, a label detecting means 804, a loweraddress subtraction means 806, an upper address subtraction means 809,an address difference calculating means 811, and a label informationresolving means 813. The machine language code generating means 802converts the optimized code 304 into machine language codes 803 that canbe executed by the processor 309. However, labels whose values have notbeen resolved are not converted and are stored in the machine languagecodes 803 as they are. The machine language code generating means 802assigns a packet address and an in-packet address to each machinelanguage code. As described later, the labels are later resolved usingthese addresses.

The label detecting means 804 finds a label that should be resolved by aPC relative value, which is to say, a difference in addresses betweentwo instructions and obtains the addresses of the branch instruction andthe branch destination instruction. After this, the label detectingmeans 804 outputs label information 805 that is composed of theinstructions that include labels and the values that resolve theselabels.

To resolve the label information 805 obtained by the label detectingmeans 804, the lower address subtraction means 806, the upper addresssubtraction means 809, and the address difference calculating means 811calculate a PC relative value as follows.

The lower address subtraction means 806 subtracts the lower 3 bits ofthe address of a branch instruction from the lower 3 bits of the addressof the branch destination instruction and outputs the carry value 807and the lower subtraction result 808.

The upper address subtraction means 809 subtracts the upper 29 bits ofthe address of a branch instruction and the carry value 807 calculatedby the lower address subtraction means 806 from the upper 29 bits of theaddress of the branch destination instruction and outputs the resultingupper subtraction result 810.

The address difference calculating means 811 finds the addressdifference 812 by setting the lower subtraction result 808 calculated bythe lower address subtraction means 806 as the lower 3 bits and theupper subtraction result 810 calculated by the upper address subtractionmeans 809 as the upper 29 bits.

The label information resolving means 813 replaces the labels in themachine language codes 803 with the address differences 812 calculatedby the address difference calculating means 811, and outputs theresulting relocatable codes 306.

The following explains a specific example of the processing of theassembler 305 on receiving an input of the optimized code 304 of FIG. 14that has been outputted by the optimization apparatus 303.

FIG. 16 is a flowchart showing the operation of the assembler.

First, the machine language code generating means 802 converts eachpacket in the optimized code 304 into machine language codes 803 thatare suited to the processor 309. However, the machine language codegenerating means 802 does not convert labels whose values have not beenresolved, so that these labels are stored as they are in the machinelanguage codes 803. After this, the machine language code generatingmeans 802 assigns packet addresses (hereafter also called “local packetaddresses”) and in-packet addresses to each instruction in the machinelanguage codes 803. FIG. 17 shows the machine language codes 803 thatare generated from the optimized code 304 shown in FIG. 14. Note thatthe actual machine language codes are expressed in binary as sequencesof zeros and ones, though for ease of understanding these machinelanguage codes are shown in FIG. 17 in mnemonic form. The parallelexecution boundary information 100 and the format information 101 willalso be clear at this stage, but are not illustrated to simplify thefigure. In FIG. 17, packet addresses (local packet addresses) areassigned starting from the value “29′h00000000”. The label f in theinstruction “jsr f” in packet 1300, the label L2 in the instruction “movL2,r2” in packet 1301, and the label L1 in the instruction “bra L1” inpacket 1302 have not yet been resolved, so that these instructions arenot converted (steps S1500, S1501).

Next, the label detecting means 804 detects labels, out of theunresolved labels in the machine language codes 803, which are locallabels that should be resolved by a PC relative value, and obtains theaddress of the instruction including the label, which is to say, thebranch instruction, and the address of the branch destinationinstruction. The label detecting means 804 then outputs labelinformation 805 that includes information showing the instructionincluding the label and the value that resolves the label. FIG. 18 showsthe label information 805 that is generated from the machine languagecodes shown in FIG. 17. Here, label L1 is detected as a local label thatshould be resolved by a PC relative value, “32′h00000012” is obtained asthe address of the branch instruction, and “32′h00000000” is obtained asthe address of the branch destination instruction (steps S1502, S1503).

The lower address subtraction means 806 then calculates the lower bitsof the value L1 that is a PC relative value. The lower addresssubtraction means 806 subtracts the lower 3 bits “3′b010” of the address“32′h00000012” of the branch instruction 1409 from the lower 3 bits“3′b000” of the address “32′h00000000” of the branch destinationinstruction 1401. As a result, “1” is obtained as the carry value 807and “3′b100” is obtained as the lower subtraction result 808 (stepS1504).

Next, the upper address subtraction means 809 calculates the upper bitsof the value L1 that is a PC relative value. The upper addresssubtraction means 809 subtracts the upper 29 bits “29′h00000002” of theaddress of the branch instruction 1409 and the carry value 807 “1” fromthe upper 29 bits “29′h00000000” of the address of the branchdestination instruction 1401. As a result, “29′h1ffffffd” (“−3” in base10, minus numbers being hereafter shown using a complement) is obtainedas the upper subtraction result 810 (step S1505).

The address difference calculating means 811 finds the addressdifference, which is to say the PC relative value, by setting the lowersubtraction result 808 as the lower bits and the upper subtractionresult 810 as the upper bits. In this example, the address differencecalculating means 811 sets “3′b100” as the lower bits and “29′h1ffffffd”as the upper bits, giving an address difference of “32′hffffffec” (stepS1506).

The label information resolving means 813 judges whether the addressdifference 812 can be expressed by only its lower 13 bits. If so, thelabel information resolving means 813 sets the lower 13 bits of theaddress difference 812 as the PC relative value, or if not, the labelinformation resolving means 813 sets the entire address difference 812as the PC relative value. As a result, a label in the machine languagecodes 803 is converted into a PC relative value. The address differencethat resolves label L1 in the label information in FIG. 17 is“32′hffffffec”, which can be expressed by the lower 13-bit value“13′fec”, so that the label L1 in the machine language codes shown inFIG. 17 is converted into the lower 13-bit value. FIG. 19 shows therelocatable codes that are generated from the machine language codes 803shown in FIG. 17. In FIG. 19, the instruction 1609 has been produced byconverting the label L1 into a PC relative value. FIG. 19 shows theparallel execution boundary information 100 and format information 101of each instruction that had already been established when the machinelanguage codes 803 were outputted, and also shows the unused bit in eachinstruction packet (steps S1507, S1508, S1509).

As described above, by finding a PC relative value by performing addresscalculation according to a carry method, an assembler corresponding to aprocessor that uses a carry method can be realized.

Linker

FIG. 20 is a block diagram showing the construction of the linker 307shown in FIG. 5 and the I/O (input/output) data of the linker 307. Thislinker 307 combines a plurality of relocatable codes 701, determines theaddresses of each instruction, and outputs the object code 714 that isexecutable by the processor 309 and is in absolute address format. Thelinker 307 includes the code combining means 702, the relocationinformation detecting means 704, the lower address subtraction means706, the upper address subtraction means 709, the address differencecalculating means 711, and the relocation information resolving means713.

The code combining means 702 combines a plurality of inputtedrelocatable codes 701 and determines the addresses of all instructions.The code combining means 702 then resolves the labels that should beresolved by instruction addresses using the determined addresses andoutputs the combined codes 703 that result from its operation.

The relocation information detecting means 704 searches for externallabels that should be resolved by PC relative addresses and obtains theaddresses of branch instructions and the branch destinationinstructions. After doing so, the relocation information detecting means704 outputs relocation information 705 includes information showinginstructions that include labels and values to be used to resolve thelabels. To resolve the resulting relocation information 705, the loweraddress subtraction means 706, the upper address subtraction means 709,and the address difference calculating means 711 calculate PC relativevalues, as described below.

The lower address subtraction means 706 subtracts the lower 3 bits ofthe address of the branch instruction from the lower 3 bits of theaddress of the branch destination instruction, and so generates a carryvalue 707 and a lower subtraction result 708.

The upper address subtraction means 709 subtracts the upper 29 bits ofthe address of the branch instruction and the carry value 707 generatedby the lower address subtraction means 706 from the upper 29 bits of theaddress of the branch destination instruction, and so generates theupper subtraction result 710.

The address difference calculating means 711 sets the lower subtractionresult 708 calculated by the lower address subtraction means 706 as thelower 3 bits and the upper subtraction result 710 calculated by theupper address subtraction means 709 as the upper 29 bits to generate theaddress difference 712.

The relocation information resolving means 713 replaces labels in thecombined codes 703 with address differences 712 calculated by theaddress difference calculating means 711, and outputs the resultingobject code 308.

The operation of the linker 307 is explained below using an examplewhere the relocatable codes 306 shown in FIG. 19 that have beenoutputted by the assembler 305 have been inputted.

FIG. 21 is a flowchart showing the operation of the linker 307.

First, the code combining means 702 combines a plurality of relocatablecodes 701. FIG. 23 shows the state when the relocatable codes 814 shownin FIG. 19 have been combined with the relocatable code shown in FIG.22. The code combining means 702 combines these relocatable codes withthe packet address of the first relocatable code in FIG. 22 as“29′h00000000” and the packet address of the first relocatable code inFIG. 19 as “29′h00000001” (step S2000, S2001).

The addresses of all instructions are determined in this way, so thatthe code combining means 702 can resolve the addresses of labels thatshould be resolved by instruction addresses and then output theresulting combined codes 703. FIG. 23 shows that the address of label L2in instruction 1810 “mov L2,r2” is the starting address of instructionpacket 1815. This address has been set at “32′h12345680”, so that thecode combining means 702 uses this value to replace the label L2. FIG.24 shows the resulting combined codes 703. In instruction 1910 in FIG.24, the label L2 has been replaced with this address “32′h12345680”(step S2002).

Next, the relocation information detecting means 704 finds externallabels in the combined codes 703 that should be resolved by PC relativevalues and extracts the addresses of the instructions that include theselabels and the addresses of the instructions where these labels arelocated, which is to say, the addresses of branch instructions andbranch destination instructions. After this, the relocation informationdetecting means 704 outputs relocation information 705 that is composedof information showing the instructions including labels and the valuesto be used to resolve these labels. FIG. 25 shows the label informationthat is generated from the combined codes 703 shown in FIG. 24. Here,label f is found as an external label that should be resolved by a PCrelative value, so that “32′h0000000a” is obtained as the address of abranch instruction and “32′h00000000” as the address of the branchdestination instruction (steps S2003, S2004).

The lower address subtraction means 706 then calculates the lower bitsof the value f that is a PC relative value. The lower addresssubtraction means 706 subtracts the lower 3 bits “3+b001” of the address“32′h0000000a” of the branch instruction 1906 from the lower 3 bits“3′b000” of the address “32′h00000000” of the branch destinationinstruction 1901. As a result, “1” is obtained as the carry value 707and “3′b100” is obtained as the lower subtraction result 708 (stepS2005).

Next, the upper address subtraction means 709 calculates the upper bitsof the value f that is a PC relative value. The upper addresssubtraction means 709 subtracts the upper 29 bits “29′h00000002” of theaddress “32′h00000000a” of the branch instruction 1906 and the carryvalue 707 “1” from the upper 29 bits “29′h00000000” of the address ofthe branch destination instruction 1901. As a result, “29′h1ffffffe” isobtained as the upper subtraction result 710 (step S2006).

The address difference calculating means 711 finds the addressdifference 712, which is to say the PC relative value, by setting thelower subtraction result 708 as the lower bits and the upper subtractionresult 710 as the upper bits. In this example, the address differencecalculating means 811 sets “3′b100” as the lower bits and “29′h1ffffffe”as the upper bits, giving an address difference of “32′hfffffff4” (stepS2007).

Next, the relocation information resolving means 713 converts a label inthe combined codes 703 into a PC relative value, setting the lower 13bits of the address difference 712 as the PC relative value if thisaddress difference 712 can be expressed by the lower 13 bits, orotherwise setting the entire address difference 712 as the PC relativevalue. The address difference that resolves the label f in therelocation information in FIG. 24 is “32′hfffffff4”, which can beexpressed by the lower 13-bit value “13′h1ff4”, so that the label f inthe combined codes 703 shown in FIG. 23 is converted into this lower13-bit value to produce the object code. The resulting object code isshown in FIG. 26. In instruction 2106 in FIG. 26, the label f has beenconverted into the lower 13-bit value “13′h1ff4” (steps S2008, S2009,S2010).

As described above, the present linker finds PC relative values using anaddress calculation including a carry, and so is suited to a processorthat uses a carry.

Specific Operation of the Processor

The following describes the operation of the processor when the objectcode shown in FIG. 26 has been stored in the instruction memory 407.

At the start of execution of this object code, the upper PC 403 is setat “29′h00000000” and the lower PC 404 is set at “3′b000”. The prefetchupper counter 410 receives an input from the upper PC 403 and so is setat “29′h00000000”.

The read of instructions from the instruction memory 407 is performed inpacket units according to the value in the prefetch upper counter 410.In detail, instruction packet 2100 that is indicated by the prefetchupper counter 410 is read from the instruction sequence stored in theinstruction memory 407 and is stored in the instruction buffer 408. Thevalue of the prefetch upper counter 410 is incremented by one in eachcycle, and so here becomes “29′h00000001”. Hereafter, an instructionpacket indicated by the prefetch upper counter 410 is read from theinstruction memory 407 and written into the instruction buffer 408 ineach cycle.

The following explains the operations for decoding and executinginstructions for the case when instruction packet 2104 is indicated bythe upper PC 403 and instruction 2107 in instruction packet 2104 isindicated by the lower PC 404. The instructions stored in theinstruction buffer 408 are interpreted by the instruction decoders 409a˜409 c. The first instruction decoder 409 a receives an input of thefirst unit, unit 2107, in the instruction packet 2104 and investigateswhether unit 2107 is a one-unit instruction and whether there is aparallel execution boundary. Since unit 2107 is a one-unit instructionand there is no parallel execution boundary, the second instructiondecoder 409 b receives an input of the next unit, unit 2109, andinvestigates whether unit 2109 is a one-unit instruction and whetherthere is a parallel execution boundary. Since unit 2109 is a one-unitinstruction and there is no parallel execution boundary, the thirdinstruction decoder 409 c receives an input of the next unit andinvestigates whether this next unit is a one-unit instruction andwhether there is a parallel execution boundary. Since this unit is not aone-unit instruction, the third instruction decoder 409 c also receivesan input of the following unit. The third instruction decoder 409 c thenfinds that this following unit includes a parallel execution boundary.As a result, the instructions 2107, 2109, and 2110 are executed inparallel.

The first instruction decoder 409 a decodes the instruction “add r0,r4”and outputs control signals to the first calculator 401 a. The firstcalculator 401 a adds the values of registers r0 and r4 and stores theresult in register r4. The second instruction decoder 409 b decodes theinstruction “and r1,r3” and outputs control signals to the secondcalculator 401 b. The second calculator 401 b performs a logicaloperation on the values of registers r1 and r3, and stores the result inregister r3. The third instruction decoder 409 c decodes the instruction“mov 32′h12345680,r2” and so has the immediate “32′h12345680”transferred into register r2.

In this case, the instruction decoders 409 a˜409 c inform the INC 412that a total of four instruction units have been executed. The INC 412increments the values in upper PC 403 and the lower PC 404 by fourunits. As a result, the lower PC 404 becomes “3′b000”, a carry of two tothe upper PC 403 is generated, and the upper PC 403 becomes“29′h00000003”. This means that the first instruction to be executed inthe next cycle is instruction 2112.

The first instruction decoder 409 a receives an input of the first unit,unit 2112, and investigates whether unit 2112 is a one-unit instructionand whether there is a parallel execution boundary. Since unit 2112 is aone-unit instruction and there is no parallel execution boundary, thesecond instruction decoder 409 b receives an input of the next unit,unit 2113, and investigates whether unit 2113 is a one-unit instructionand whether there is a parallel execution boundary. Here, the secondinstruction decoder 409 b finds that unit 2109 is a one-unit instructionand that there is a parallel execution boundary. As a result, theprocessor 309 finds that instructions 2112 and 2113 can be executed inparallel.

The first instruction decoder 409 a decodes the instruction “ld(r2),r0”, has the operand data, which has the value in register r2 asthe operand address, read from the data memory 406 and stored inregister r0. The second instruction decoder 409 b decodes theinstruction “bra 13′h1fec”, and, since this is a branch instruction,updates the values in the upper PC 403 and lower PC 404 using theaddress of the branch destination instruction.

First, the address indicated by the upper PC 403 and lower PC 404 isamended. While a PC relative value shows the difference in addressesbetween a branch instruction and its branch destination instruction, theupper PC 403 and lower PC 404 show the address of the first address tobe executed in the same cycle as the branch instruction, so that theupper PC 403 and lower PC 404 are amended so that they indicate theaddress of the branch instruction. In detail, the INC 412 increments thevalues of the upper PC 403 and lower PC 404 by one unit to show that thebranch instruction 2113 is preceded by one instruction unit, the firstinstruction 2112. As a result, the lower PC 404 becomes “3′b010” and theupper PC 403 stays at “29′h00000003”.

Following this, the upper PC calculator 411 and the lower PC calculator405 add the PC relative value “13′h1fec” obtained by the secondinstruction decoder 409 b to the upper PC 403 and the lower PC 404.Here, the sign-extended 32-bit value “32′hffffffec” is used as the PCrelative value. This addition is split into additions of the upper 29bits and the lower 3 bits.

The lower PC calculator 405 adds the lower 3 bits “3′b100” of the PCrelative value to the value “3′b010” of the lower PC 404. As a result, acarry of one and the lower calculation result “3′b000” are obtained. Thelower PC calculator 405 sends the carry to the upper PC calculator 411,and sends the lower calculation result to the lower PC 404.

Next, the upper PC calculator 411 adds the upper 29 bits “29′h1ffffffd”of the PC relative value and the carry value “1” received from the lowerPC calculator 405 to the value “29′h00000003” of the upper PC 403. Theupper PC calculator 411 sends the upper calculation result of“29′h00000001” to the upper PC 403, which sends the value on to theprefetch upper counter 410. As a result of this processing, the prefetchupper counter 410 is set at “29′h00000001” so that the next instructionpacket to be prefetched will be instruction packet 2104. Also, since theupper PC 403 is “29′h00000001” and the lower PC 404 is “3′b000”, thefirst instruction to be executed in the next cycle is instruction 2105.

Hereafter, codes in the object code are successively read and executedin the same way, so that no explanation will be given for the otherinstructions.

This completes the detailed explanation of the constructions of theprocessor 309, linker 307, assembler 305 and optimization apparatus 303shown in FIG. 5. A conventional compiler can be used as the compiler301, so that no explanation of such will be given.

Note that while the processor of this embodiment includes threeinstruction decoders 409 a˜409 c and three calculators 401 a˜401 c, thepresent invention is not limited to this construction, so that only oneinstruction decoder and one calculator may by provided. It is alsopossible for the functions of the optimization apparatus 303 to beincorporated into the compiler 301, and to have the object code 308generated from the source code 300 by the compiler 301, the assembler305, and the linker 307.

In the present embodiment, the prefetch lower counter 413 was describedas having the fixed value of “3′b000”, though this need not be the case.As one example, this value may be incremented by one in each cycle. Thisresults in one byte of data being read from the instruction memory 407and written into the instruction buffer 408 in each cycle.

Second Embodiment

The second embodiment of the present invention relates to a modificationof the processor, optimization apparatus, assembler, and linker of thefirst embodiment. This modification uses a different value as the PCrelative value for resolving labels in branch instructions.

In the first embodiment, the PC relative value in a branch instructionis a difference in addresses between the branch instruction and thebranch destination instruction, while in this second embodiment, the PCrelative value in a branch instruction is a difference between theaddress of the branch destination instruction and the address of thefirst instruction in same set of instructions as the branch instruction.

In this way, the PC relative value has a slightly different meaning thanin the present embodiment. However, if the devices used to generate aprogram (i.e., the optimization apparatus 303, assembler 305, and linker307 that calculate the PC relative value) use the same meaning as thedevice that executes the program (i.e., a processor that calculates anaddress based on the PC relative value), the processor will be able tocorrectly change the program counter to the address of a branchdestination instruction when executing a branch instruction.

The following explains the optimization apparatus 303, assembler 305,linker 307, and processor.

The label detecting means 905 of the optimization apparatus 303generates the label information 906 for labels that should be resolvedby PC relative values in the following way. Instead of generating labelinformation after obtaining the provisional addresses of the branchinstruction and the branch destination instruction in the same way as inthe first embodiment, the label detecting means 905 generates the labelinformation 906 after obtaining the provisional addresses of the branchdestination instruction and the address of the first instruction in thesame set of instructions as the branch instruction. In the same way asin the first embodiment, this label information 906 is then used tocalculate the address difference 913 that is the difference between twoprovisional addresses and is used in the optimized code 304. Theassembler and linker also operate in this way.

The following describes a specific example of the object code 308generated in this embodiment.

The assembler 305 replaces the label L1 in instruction 1409 in themachine language codes shown in FIG. 17 with the subtraction value“13h′1ff0” produced by subtracting the address “32′h00000010” ofinstruction 1408, which is the first instruction in same set ofinstructions as instruction 1409, from the address “32′h00000000” of thebranch destination instruction. In the same way, the linker 307 replacesthe label f in instruction 1906 in the combined codes shown in FIG. 24with the subtraction value “13′h1ff8” produced by subtracting theaddress “32′h00000008” of the instruction 1907, which is the firstinstruction in same set of instructions as instruction 1906, from theaddress “32′h00000000” of the branch destination instruction. FIG. 27shows that the PC relative value of instruction 2213 differs from thatshown in FIG. 26.

The following describes the processor of the present embodiment.

The processor 309 executes object code that have been generated asdescribed above. When the processor 309 executes a branch instruction,the PC relative value in the branch instruction is a difference inaddresses between the branch destination instruction and the firstinstruction in same set of instructions as the branch instruction.Accordingly, the processor 309 does not amend the values of the upper PC403 and lower PC 404, and, in the same way as in the first embodiment,adds the PC relative value to the values in the upper PC 403 and lowerPC 404 and updates the values in the upper PC 403 and lower PC 404 usingthe addition results. When this processor 309 executes the object codeshown in FIG. 27, the execution of instruction 2213 results in the PCrelative value “13′h1ff8” being added to the present PC “32′h00000008”,resulting in the PC being updated to “32′h00000000”.

As described above, the processor of the present embodiment does notneed to amend the value of the program counter in the same way as in thefirst embodiment whenever a branch instruction is executed. The addressof a branch destination instruction can instead be obtained by directlyadding a PC relative value to the PC. This reduces the total executiontime.

Third Embodiment

The third embodiment of the present invention relates to a processorthat can indicate the execution position of an instruction by fullyutilizing the lower 3 bits of instruction addresses.

In the first embodiment, the lower 3 bits of the instruction address areused to indicate a position that is one of three units. In the presentembodiment, however, full use is made of these 3 bits by having themindicate one of eight units.

FIG. 28A shows the construction of an instruction packet in the presentembodiment. This instruction packet is composed of eight instructionunits. Each instruction unit in an instruction packet is 8 bits long, sothat the total length of one instruction packet is 64 bits. Theprocessor in this embodiment reads one instruction packet (64 bits) inone cycle.

FIG. 28B shows the types of instructions used in this embodiment. Eachinstruction is composed of 8-bit instruction units, with there beingone-, two-, three-, four-, five-, and six-unit instructions.

FIG. 28C shows the relation between in-packet addresses and theinstruction units in a packet. In the same way as in the firstembodiment, a position in an instruction packet is indicated by thelower 3 bits of an instruction address. As shown in FIG. 28C, thein-packet address “3′b000” indicates the first unit, the in-packetaddress “3′b001” indicates the second unit, the in-packet address“3′b010” indicates the third unit, the in-packet address “3′b011”indicates the fourth unit, the in-packet address “3′b100” indicates thefifth unit, the in-packet address “3′b101” indicates the sixth unit, thein-packet address “3′b110” indicates the seventh unit, and the in-packetaddress “3′b111” indicates the eighth unit.

As described above, the processor of the present embodiment indicatesthe execution position of an instruction making full use of the lower 3bits of the instruction address. As a result, instructions can beexecuted with a greater variation of execution units for one cycle.

Fourth Embodiment

The fourth embodiment of the present invention relates to a method forcalculating instruction addresses without using a carry.

The first embodiment teaches a processor for executing a program, and anoptimization apparatus, assembler, and linker for generating a suitableprogram. All of these devices use a common method for calculating aninstruction address using a carry. This has the effect that theprocessor can correctly generate the address of a branch destinationinstruction using a PC relative value. However, this effect can beachieved if the processor, optimization apparatus, assembler, and linkeruse a common address calculation method that does not use a carry. Thispresent embodiment relates to such a calculation method that calculatesaddresses without using a carry.

This calculation method that does not use a carry resembles thecalculation method in the first embodiment in that the calculation ofaddress is performed separately for the upper 29 bits and lower 3 bits.However, the present method differs by not using a carry.

The following explains the method by which the processor finds theaddress of a branch destination instruction by adding the address of abranch instruction and a PC relative value. The lower PC calculator 405shown in FIG. 6 adds the lower 3 bits of the address of the branchinstruction and the lower 3 bits of the PC relative value. FIG. 29A isan addition table showing the addition rules for adding the lower 3 bitsof the address of the branch instruction and the lower 3 bits of the PCrelative value in the present calculation method. As shown in thefigure, this calculation differs from a normal addition of binary valuesin that it cycles between the three states “3′b000”, “3′b010”, and“3′b100”. Note that no carry is generated.

The upper PC calculator 411 shown in FIG. 6 adds the upper 29 bits ofthe address of the branch instruction and the upper 29 bits of the PCrelative value. This is a normal addition of binary values.

The results of the above additions form the address of a branchdestination instruction. In detail, the addition result for the lower 3bits is set in the lower PC 404 and the addition result for the upper 29bits is set in the upper PC 403.

The following explains the method used by the optimization apparatus,assembler, and linker to calculate the PC relative value, which is tosay, to subtract the address of the branch destination instruction fromthe address of the branch instruction. This subtraction is split into anupper 29 bits and lower 3 bits like the addition performed by theprocessor. The lower address subtraction means 907 of the optimizationapparatus 303, the lower address subtraction means 806 of the assembler305, and the lower address subtraction means 706 of the linker 307subtract the lower 3 bits of the address of a branch instruction fromthe lower 3 bits of the address of the branch destination instruction.FIG. 29B is a subtraction table showing the subtraction rules forsubtracting the lower 3 bits of the address of the branch instructionfrom the lower 3 bits of the address of the branch destinationinstruction. As shown in the figure, this calculation differs from anormal subtraction of binary values in that it cycles between the threestates “3′b000”, “3′b010”, and “3′b100”. Note that no carry isgenerated.

The upper address subtraction means 910 of the optimization apparatus303, the upper address subtraction means 809 of the assembler 305, andthe upper address subtraction means 709 of the linker 307 subtract theupper 29 bits of the address of the branch instruction from the upper 29bits of the address of the branch destination instruction. This is anormal subtraction of binary values.

The PC relative value is then found by setting the result of the abovesubtraction for the lower 3 bits as the lower 3 bits and the result ofthe above subtraction for the upper 29 bits as the upper 29 bits.

FIG. 30 shows the object code that is generated by the above addresscalculation method of the present embodiment that does not use a carry.The PC relative values of instructions 2406 and 2413 differ to those inFIG. 26. The following explains the calculation of the PC relative valueof instruction 2406.

The lower address subtraction means 706 subtracts the lower 3 bits“3′b010” of the address of instruction 2406 from the lower 3 bits“3′b000” of the address of instruction 2401 in accordance with thesubtraction table shown in FIG. 29B. This produces the lower subtractionresult “3′b100”.

The upper address subtraction means 709 subtracts the upper 29 bits“29′h00000001” of the address of instruction 2406 from the upper 29 bits“29′h00000000” of the address of instruction 2401. This produces theupper subtraction result “29′h1fffffff”.

The address difference calculating means 711 generates the addressdifference “32′h1ffffffc” by setting the upper subtraction result“29′h1fffffff” as the upper 29 bits and the lower subtraction result“3′b100” as the lower 3 bits.

The relocation information resolving means 713 judges that the addressdifference “32′h1ffffffc” can be expressed by just the lower 13 bits“13′h1ffc” and so replaces a label with this value “3′h1ffc” as a PCrelative value to generate instruction 2406.

The processor 309 executes the object code generated as described above.When executing a branch instruction, the processor 309 adds the upper PC403 and lower PC 404, which have been amended to correctly indicate thebranch instruction, to the PC relative value in the branch instructionwithout generating a carry.

When the processor 309 executes instruction 2406 in the object codeshown in FIG. 30, the lower PC calculator 405 adds the amended lower PC404 “3′b010” and the lower 3 bits “3′b100” of the PC relative value andupdates the lower PC 404 to the resulting addition value “3′b000”. Theupper PC calculator 411 adds the amended upper PC 403 “29′h00000001” andthe upper 29 bits “29′h1fffffff” of the PC relative value and updatesthe lower PC 404 to the resulting addition value “29′h00000000”.

As described above, the present calculation method can calculateaddresses without a carry being sent between the lower PC calculator 405and the upper PC calculator 411. This means that address calculation canbe performed with a simpler hardware construction.

Fifth Embodiment

The fifth embodiment of the present invention teaches a method forcalculating instruction addresses using absolute values.

This calculation method that uses absolute values resembles thecalculation method in the first embodiment in that the calculation ofaddress is performed separately for the upper 29 bits and lower 3 bits.However, the present method differs from the carry method in that thevalue of the lower 3 bits of an instruction address are set as the lower3 bits of the calculation result.

The following explains the method by which the processor finds theaddress of a branch destination instruction by adding the address of abranch instruction and a PC relative value. The lower PC calculator 405shown in FIG. 6 adds the lower 3 bits of the address of the branchinstruction and the lower 3 bits of the PC relative value. FIG. 31A isan addition table showing the addition rules for adding the lower 3 bitsof the address of the branch instruction and the lower 3 bits of the PCrelative value in the present calculation method that uses absolutevalues. As shown in the figure, the lower 3 bits of the PC relativevalue are set as the lower 3 bits of the addition result.

The upper PC calculator 411 shown in FIG. 6 adds the upper 29 bits ofthe address of the branch instruction and the upper 29 bits of the PCrelative value. This is a normal addition of binary values.

The results of the above additions form the address of a branchdestination instruction. In detail, the addition result for the lower 3bits is set in the lower PC 404 and the addition result for the upper 29bits is set in the upper PC 403.

The following explains the method used by the optimization apparatus303, assembler 305, and linker 307 to calculate the PC relative value,which is to say, to subtract the address of the branch destinationinstruction from the address of the branch instruction. This subtractionis split into an upper 29 bits and lower 3 bits, like the additionperformed by the processor. The lower address subtraction means 907 ofthe optimization apparatus 303, the lower address subtraction means 806of the assembler 305, and the lower address subtraction means 706 of thelinker 307 subtract the lower 3 bits of the address of a branchinstruction from the lower 3 bits of the address of the branchdestination instruction. FIG. 31B is a subtraction table showing thesubtraction rules for subtracting the lower 3 bits of the address of thebranch instruction from the lower 3 bits of the address of the branchdestination instruction in this calculation method that uses absolutevalues. As shown in the figure, the lower 3 bits of the branchdestination address are set as the subtraction result for the lower 3bits.

The upper address subtraction means 910 of the optimization apparatus303, the upper address subtraction means 809 of the assembler 305, andthe upper address subtraction means 709 of the linker 307 subtract theupper 29 bits of the address of the branch instruction from the upper 29bits of the address of the branch destination instruction. This is anormal subtraction of binary values.

The PC relative value is then found by setting the result of the abovesubtraction for the lower 3 bits as the lower 3 bits and the result ofthe above subtraction for the upper 29 bits as the upper 29 bits.

FIG. 32 shows the object code that is generated by the above addresscalculation method of the present embodiment that uses absolute values.The PC relative values of instructions 2606 and 2613 differ to those inFIG. 26. The following explains the calculation of the PC relative valueof instruction 2606.

The lower address subtraction means 706 subtracts the lower 3 bits“3′b010” of the address of instruction 2406 from the lower 3 bits“3′b000” of the address of instruction 2401 in accordance with thesubtraction table shown in FIG. 31B. This produces the lower subtractionresult “3′b000”.

The upper address subtraction means 709 subtracts the upper 29 bits“29′h00000001” of the address of instruction 2406 from the upper 29 bits“29′h00000000” of the address of instruction 2401. This produces theupper subtraction result “29′h1fffffff”.

The address difference calculating means 711 generates the addressdifference “32′h1ffffff8” by setting the upper subtraction result“29′h1fffffff” as the upper 29 bits and the lower subtraction result“3′b000” as the lower 3 bits.

The relocation information resolving means 713 judges that the addressdifference “32′h1ffffff8” can be expressed by just the lower 13 bits“13′h1ff8” and so replaces a label with this value “13′h1ff8” as a PCrelative value to generate instruction 2606.

The processor 309 executes the object code generated as described above.When executing a branch instruction, the processor 309 adds the upper PC403 and lower PC 404, which have been amended to correctly indicate thebranch instruction, to the PC relative value in the branch instructionusing the present absolute value method.

When the processor 309 executes instruction 2606 in the object codeshown in FIG. 32, the lower PC calculator 405 adds the amended lower PC404 “3′b010” and the lower 3 bits “3′b000” of the PC relative value andupdates the lower PC 404 to the resulting addition value “3′b000”. Theupper PC calculator 411 adds the amended upper PC 403 “29′h000000001”and the upper 29 bits “29′h1fffffff” of the PC relative value andupdates the lower PC 404 to the resulting addition value “29′h00000000”.

As described above, the present calculation method can calculateaddresses without needing to calculate the lower bits, so that the speedfor calculating addresses can be improved.

Sixth Embodiment

The sixth embodiment of the present invention relates to a linearcalculation method for addresses. Unlike the other embodiments, thislinear calculation method calculates instruction addresses withoutsplitting the calculation into an upper 29 bits and lower 3 bits.

The following explains the present method for finding the address of abranch destination instruction from the address of a branch instructionand a PC relative value. While the processor that uses the carry methodis equipped with an upper PC calculator 411 for calculating the upper 29bits and a lower PC calculator 405 for calculating the lower 3 bits, aprocessor that uses the present linear calculation method is onlyequipped with one PC calculator for calculating a 32-bit address. The PCcalculator in this linear calculation method adds a 32-bit address of abranch instruction and a 32-bit PC relative value. This calculation is anormal binary addition.

The addition result of the PC calculator is set as the address of thebranch destination instruction. This means that the lower 3 bits of theaddition result are set in the lower PC 404 and the upper 29 bits of theaddition result are set in the upper PC 403.

The following explains the calculation of the PC relative value by theoptimization apparatus 303, assembler 305, and linker 307, which is tosay, the subtraction of the address of the branch instruction from theaddress of the branch destination instruction. Like the processor inthis embodiment, the optimization apparatus 303, assembler 305, andlinker 307 are each provided with only one calculator, the addresssubtraction means, for calculating a 32-bit address. The addresssubtraction means in this linear calculation method subtracts theaddress of a branch instruction from the address of a branch destinationinstruction. This calculation is a normal binary subtraction. Thesubtraction result is then set as the PC relative value.

FIG. 33 shows the object code that has been generated using the linearcalculation method of the present embodiment. In FIG. 33, the PCrelative values in instructions 2706 and 2713 differ to those shown inFIG. 26. The following describes the method for calculating the PCrelative value for instruction 2706.

The address subtraction means in the linear calculation method subtractsthe 32-bit address “32′h00000000” of instruction 2701 from the 32-bitaddress “32′h0000000a” of instruction 2706 and so obtains the addressdifference “32′hfffffff6”.

The relocation information resolving means 713 judges that the addressdifference “32′hfffffff6” can be expressed by just its lower 13 bits“13′h1ff6”, and so replaces the label with “13′h1ff6” as the PC relativevalue to generate instruction 2706.

The processor 309 executes the object code generated as described above.When executing a branch instruction, the processor 309 adds the upper PC403 and lower PC 404 that have been amended to indicate the address ofthe branch instruction to the PC relative value using the present linearcalculation method.

When the processor 309 executes instruction 2706 in the object codeshown in FIG. 33, the PC calculator in this embodiment adds a 32-bit PCvalue “32′h0000000a”, which has the amended value of the upper PC 403 asthe upper 29 bits and the amended value of the lower PC 404 as the lower3 bits, to the PC relative value “32′hfffffff6” and so obtains theaddition result “32′h00000000”. After this, the PC calculator updatesthe lower PC 404 to the lower 3 bits “3′b000” of this addition value,and the upper PC 403 to the upper 29 bits “29′h00000000” of thisaddition value.

In this way, the present linear calculation method can calculateaddresses using a standard calculator as the PC calculator. Thissimplifies the structure of the processor.

Seventh Embodiment

The seventh embodiment of the present invention relates to a processorthat interprets and executes PC adding instructions and PC subtractinginstructions and to a compiler that generates such instructions.

FIG. 34 shows the processor of the present embodiment. The processor ofthe present embodiment differs from the processor in the firstembodiment in that it further includes a second lower PC calculator 2800and a second upper PC calculator 2802 and in that the first instructiondecoder 2801 a, the second instruction decoder 2801 b, and the thirdinstruction decoder 2801 c are all provided with new functions.

The instruction decoders 2801 a˜2801 c are provided with an extrafunction for decoding PC adding instructions and PC subtractinginstructions. FIG. 35A shows the operation that corresponds to a PCadding instruction which is shown in mnemonic form. As shown in FIG.35A, a PC adding instruction adds a PC relative value “disp” to thevalue of the PC that is stored in a register and stores the additionresult in the same register. FIG. 35B shows the operation thatcorresponds to a PC subtracting instruction which is shown in mnemonicform. As shown in FIG. 35B, a PC adding instruction subtracts a PCrelative value “disp” from the value of the PC that is stored in aregister and stores the subtraction result in the same register.

The second lower PC calculator 2800 and the second upper PC calculator2802 perform the PC adding instruction and PC subtraction instructiondescribed above, using the same calculation rules as the lower PCcalculator 405 and the upper PC calculator 411 described in the firstembodiment.

FIG. 36 shows the construction of the compiler of the presentembodiment.

The source code 2901 is a program written in a high-level language suchas C.

The intermediate code converting unit 2902 converts the source code 2901into intermediate code 2903 which is an internal expression for thecompiler. This intermediate code converting unit 2902 is a well-knowntechnology and so will not be described.

The PC value adding instruction converting unit 2904 converts eachintermediate code in the intermediate code 2903 that adds a value of thePC and a variable into an assembler code 2906 for a PC addinginstruction that is shown in FIG. 34.

The instruction converting unit 2905 converts the other intermediatecodes into assembler code 2906. This instruction converting unit 2905 isa well-known technology and so will not be described.

The following describes a specific example of the operation of thepresent compiler. FIG. 37 is a flowchart showing the operation of thiscompiler.

First, the compiler receives an input of source code. FIG. 38 showssource code which is written in C language. In FIG. 38, the externalfunctions g1, g2, g3, and g4 are declared, and the function f is definedas a function that receives the int-type variable “i”. This function fincludes code that substitutes the address of function g1 into thepointer fp if the value of “i” is 1, substitutes the address of functiong2 into the pointer fp if the value of “i” is 2, substitutes the addressof function g3 into the pointer fp if the value of “i” is 3, substitutesthe address of function g4 into the pointer fp if the value of “i” is 4,and finally calls the function indicated by the pointer fp (step 3600).

Next, the intermediate code converting unit 2902 converts the sourcecode into intermediate codes. When doing so, the intermediate codeconverting unit 2902 coverts (a) a source code that substitutes apointer to an external function into a pointer variable into (b) anintermediate code that adds the difference between the address of thestart of present function and the address of the start of the externalfunction to a temporary variable that stores the address of the start ofthe present function, and substitutes the addition result into thepointer variable.

FIG. 39 shows the intermediate codes that have been generated from thesource program shown in FIG. 38. The intermediate code 3201 shown inFIG. 39 is an intermediate code that has the label f marking the startof the function and that substitutes the present value of the PC, whichis to say, the first address of function f, into the temporary variabletmp. The intermediate code 3202 is intermediate code that judges whetherthe value of variable i is not “1”. The intermediate code 3203 is anintermediate code that branches to the label L when the judgement byintermediate code 3203 is true, that is, variable i is not “1”. Theintermediate code 3204 is executed when variable i is “1”, and adds adifference, obtained by subtracting a first address of function f fromthe first address of function g1, to the temporary variable tmp intowhich the first address of function f has been substituted, and has theaddition result substituted into the variable fp. The intermediate code3205 is an intermediate code that branches to the label L.

The intermediate code 3206 includes the label L1, and is an intermediatecode that judges whether variable i is not equal to “2”. Theintermediate code 3207 branches to label L2 when the judgement inintermediate code 3206 is true, which is to say, when variable i is not“2”. The intermediate code 3208 is executed when variable i is equal to“2”, and is an intermediate code that adds a difference, obtained bysubtracting a first address of function f from the first address offunction g2, to the temporary variable tmp into which the first addressof function f has been substituted, and has the addition resultsubstituted into the variable fp. The intermediate code 3209 is anintermediate code that branches to the label L.

The intermediate code 3210 includes the label L2, and is an intermediatecode that judges whether variable i is not equal to “3”. Theintermediate code 3211 branches to label L3 when the judgement inintermediate code 3210 is true, which is to say, when variable i is not“3”. The intermediate code 3212 is executed when variable i is equal to“3”, and is an intermediate code that adds a difference, obtained bysubtracting a first address of function f from the first address offunction g3, to the temporary variable tmp into which the first addressof function f has been substituted, and has the addition resultsubstituted into the variable fp. The intermediate code 3213 is anintermediate code that branches to the label L.

The intermediate code 3214 includes the label L4, and is an intermediatecode that adds a difference, obtained by subtracting a first address offunction f from the first address of function g4, to the temporaryvariable tmp into which the first address of function f has beensubstituted, and has the addition result substituted into the variablefp. The intermediate code 3215 includes the label L and is anintermediate code that calls the function indicated by the variable fp.

As described above, the intermediate codes in FIG. 39 do not simplysubstitute the absolute address of the function g1, g2, g3 or g4 intothe variable fp, but instead add a difference between the first addressof function f and the first address of one of the functions g1, g2, g3,and g4 to the first address of the function f and substitute theaddition result into the variable fp (steps S3601˜S3603).

Next, the PC value adding instruction converting unit 2904 converts theintermediate codes into assembler code. The PC value adding instructionconverting unit 2904 searches for intermediate codes that add the valueof the PC to a PC relative value and converts such codes into assemblercode that uses the second lower PC calculator 2800 and the second upperPC calculator 2802. The instruction converting unit 2905 then convertsthe remaining intermediate codes into assembler code.

The PC value adding instruction converting unit 2904 ascertains that theoperand tmp in intermediate code 3204 in FIG. 39 has been set at thevalue of the PC by the intermediate code 3201 and that the operator “+”indicates an addition of the value of the PC and a PC relative value,and so converts intermediate code 3204 into the assembler code addpcthat performs an addition using the second lower PC calculator 2800 andthe second upper PC calculator 2802. In the same way, the PC valueadding instruction converting unit 2904 converts intermediate codes3208, 3212, and 3214 into assembler codes addpc. The other intermediatecodes in FIG. 39 are converted into assembler codes by the instructionconverting unit 2905.

FIG. 40 shows the assembler code that has been produced by convertingthe intermediate codes shown in FIG. 39. In FIG. 40, the assembler code3301 has the label f marking the start of a function and is aninstruction that transfers the value of the PC into register r1. Theassembler code 2802 is an instruction that judges whether the constant“1” and the value of register r0 are not equal. The assembler code 3303is an instruction that branches to label L1 when the judgement inassembler code 2802 is true. The assembler code 3304 has the secondlower PC calculator 2800 and the second upper PC calculator 2802 add thePC relative value that is the difference between the first address offunction g1 and the first address of function f to the value of the PCwhich is the first address of function f and is stored in the registerr1, and has the result transferred into register r1. The assembler code3305 is an instruction that branches to the label L.

The assembler code 3306 has the label L1 and is an instruction thatjudges whether the constant “2” and the value of register r0 are notequal. The assembler code 3307 is an instruction that branches to labelL2 when the judgement in assembler code 3306 is true. The assembler code3308 has the second lower PC calculator 2800 and the second upper PCcalculator 2802 add the PC relative value that is the difference betweenthe first address of function g2 and the first address of function f tothe value of the PC which is the first address of function f and isstored in the register r1, and has the result transferred into registerr1. The assembler code 3309 is an instruction that branches to the labelL.

The assembler code 3310 has the label L2 and is an instruction thatjudges whether the constant “3” and the value of register r0 are notequal. The assembler code 3311 is an instruction that branches to labelL3 when the judgement in assembler code 3310 is true. The assembler code3311 has the second lower PC calculator 2800 and the second upper PCcalculator 2802 add the PC relative value that is the difference betweenthe first address of function g3 and the first address of function f tothe value of the PC which is the first address of function f and isstored in the register r1, and has the result transferred into registerr1. The assembler code 3313 is an instruction that branches to the labelL.

The assembler code 3314 has the label L3 and is an instruction that hasthe second lower PC calculator 2800 and the second upper PC calculator2802 add the PC relative value that is the difference between the firstaddress of function g4 and the first address of function f to the valueof the PC which is the first address of function f and is stored in theregister r1, and has the result transferred into register r1. Theassembler code 3315 has the label L and is an instruction that calls thefunction indicated by register r1. The assembler code 3316 is aninstruction that ends the function.

As described above, when there is a source code in function f thatsubstitutes a pointer to the external function g into a pointervariable, the present compiler does not generate an instruction (such as“mov r1,g”) that transfers the address of the external function g intoregister r1, but instead generates an instruction (addpc g-f, r1) thathas adds a difference (g-f) in addresses between function f and functiong to the address of function f that is stored in register r1, and hasthe result transferred into register r1. Since the value of the PCrelative value g-f is smaller that the absolute address g, the overallcode size of programs can be reduced by using such addpc instructions.This has a further benefit for PIC codes where the addresses of aprogram in memory are determined when the program is executed, sincecalculation instructions that use such PC relative values must be used.

In the same way as in the first embodiment, the assembler code producedby the compiler of the present embodiment is converted into object codethat can be executed by the processor by an optimization apparatus 303,an assembler 305 and a linker 307. The processor executes the PC addinginstruction “addpc g-f,r1” in the generated object code using the secondlower PC calculator 2800 and the second upper PC calculator 2802. Indetail, the second lower PC calculator 2800 adds the lower 3 bits of theconstant “g-f” and the lower 3 bits of the value stored in register r1and sends any carry that is generated to the second upper PC calculator2802. The second upper PC calculator 2802 adds the upper 29 bits of theconstant “g-f”, the upper 29 bits of the value stored in register r1,and any carry it has received from the second lower PC calculator 2800.A value given by setting the addition result of the second lower PCcalculator 2800 as the lower 3 bits and the addition result of thesecond upper PC calculator 2802 as the upper 29 bits is then set inregister r1.

Note that while the instructions shown in FIGS. 35A and 35B respectivelyare an addition and a subtraction of a constant and the value in aregister, this need not be the case. An addition and a subtraction ofvalues in registers, or an addition and a subtraction of a value in aregister and the PC may equally be used.

The calculation method used by the second lower PC calculator 2800 andthe second upper PC calculator 2802 also need not be the carry methodused in the first embodiment. Provided the same method is used by theoptimization apparatus 303, assembler 305, and linker 307 that generatethe object code to be executed by the processor, any of a no-carrymethod, a linear method, and an absolute value method may be used.

Eighth Embodiment

The eighth embodiment of the present invention relates to a debugger anda disassembler.

FIG. 41 is a block diagram showing the construction of the debugger anddisassembler of the present embodiment.

The input control unit 4000 receives an input from the user and controlsthe other components according to this input.

The packet address specifying unit 4001 calculates the upper 29 bits ofthe address of the inputted instruction.

The in-packet address specifying unit 4002 calculates the lower 3 bitsof the address of the inputted instruction.

The instruction memory 4004 stores the instructions to be processed bythe debugger and disassembler. As in the first embodiment, the addressesof instructions are 32 bits in length and are composed of a packetaddress as the upper 29 bits and an in-packet address as the lower 3bits. FIG. 41 shows how the instructions shown in FIG. 25 are stored.

The instruction reading unit 4003 reads an instruction packet indicatedby the packet address specified by the packet address specifying unit4001 from the instruction memory 4004.

The instruction buffer 4005 stores the instruction packet read from theinstruction memory 4004 by the instruction reading unit 4003.

The instruction decoding unit 4006 extracts the instruction unit withthe in-packet address specified by the in-packet address specifying unit4002 from the instruction buffer 4005 and decodes the extractedinstruction unit. When the instruction unit is a branch instruction, theinstruction decoding unit 4006 sends the PC relative value 4007 to thelower PC calculator 4008 and the upper PC calculator 4009.

The label table 4011 is a table storing each label name associated witha corresponding instruction address. This label table 4011 is generatedby extracting information from the optimized code when the assemblerdescribed in the first embodiment generates machine language codes.

In FIG. 41, the address “32′h00000000” corresponds to the label f, theaddress “32′h00000008” corresponds to the label L1, and the address“32′h12345680” corresponds to the label L2.

The display unit 4012 displays the results of a disassembling of aninstruction.

The instruction replacing unit 4013 writes the instruction that has beenreplaced into the instruction unit(s) in the instruction buffer 4005that is/are indicated by the in-packet address specified by thein-packet address specifying unit 4002.

The instruction writing unit 4014 rewrites the instruction packet in theinstruction memory 4004 with the packet address specified by the packetaddress specifying unit 4001 using the amended instruction packet storedin the instruction buffer 4005.

The upper PC calculator 4009 performs a calculation on the upper 29 bitsof the instruction address specified by the packet address specifyingunit 4001 and the upper 29 bits of the PC relative value 4007.

The lower PC calculator 4008 performs a calculation on the lower 3 bitsof the instruction address specified by the in-packet address specifyingunit 4002 and the lower 3 bits of the PC relative value 4007. Thecalculation methods used by these PC calculators is the same as thatused when generating the object code.

The following describes a specific example of the operation of thepresent disassembler. FIG. 42 is a flowchart showing the operatingprocedure of this disassembler.

First, the input control unit 4000 receives a command indicating thedisassembling of an instruction and an input of the address of theinstruction to be disassembled. In this specific example, the inputcontrol unit 4000 receives “32′h0000001a” as the instruction address(step S4100).

Next, the packet address specifying unit 4001 specifies the packetaddress from the upper 29 bits of the instruction address. Theinstruction reading unit 4003 then reads the instruction packet with thespecified packet address from the instruction memory 4004 and stores itin the instruction buffer 4005. In this example, “29′h00000003” isspecified as the packet address, and the instruction sequence “ld(r2),r0∥bra 13′h1fec∥add r2,r3” is stored in the instruction buffer 4005(step S4101).

The in-packet address specifying unit 4002 then specifies the in-packetaddress from the lower 3 bits of the instruction address and informs theinstruction decoding unit 4006 of the instruction unit that has thespecified in-packet address. The instruction decoding unit 4006 thenextracts the indicated instruction unit from the instruction buffer4005. In this example, “3′b010” is specified as the in-packet addressand the instruction “bra 13′h1fec” that is the second unit in theinstruction buffer 4005 is inputted into the instruction decoding unit4006 (step S4102).

The instruction decoding unit 4006 judges whether the inputtedinstruction is a branch instruction. In this example, the inputtedinstruction “bra 13′h1fec” is a branch instruction, so that thisjudgement is true (step S4103).

When the instruction is a branch instruction, a calculation is performedon the PC relative value 4007 indicated in the instruction and addressof the inputted instruction. The lower PC calculator 4008 performs anaddition or a subtraction on the in-packet address of the inputtedinstruction and on the lower 3 bits of the PC relative value 4007 andsends the calculation result to the label search unit 4010. The upper PCcalculator 4009 performs an addition or a subtraction on the packetaddress of the inputted instruction and on the upper 29 bits of the PCrelative value 4007 and sends the calculation result to the label searchunit 4010. The label search unit 4010 specifies the address of a labelfrom the calculation result for the upper bits and the calculationresult for the lower bits. In this example, the label address“32′h00000008” is specified by a calculation using the address“32′h0000001a” of the inputted instruction and the PC relative value4007 “13′h1fec” (steps S4103, S4104).

The label search unit 4010 then refers to the label table 4011 and findsthe label name that has the specified address. In this example, thelabel L1 corresponds to the address “32′h00000008” (Step S4107).

The display unit 4012 displays the assembler name of the branchinstruction and the label name found by the label search unit 4010. Inthis example, the display unit 4012 displays the assembler name “bra” ofthe branch instruction and the corresponding label name “Label L1” (StepS4108).

The instruction decoding unit 4006 has the display unit 4012 displayonly the assembler name when the extracted instruction is not anassembler instruction (Step S4109).

The following describes a specific example of the operation of thepresent debugger.

FIG. 43 is a flowchart showing the operation of the present debugger.

First, the input control unit 4000 receives a command indicating thedebugging of an instruction, the address of an instruction to bereplaced, and the instruction to be used to replace of this instruction.In this specific example, the input control unit 4000 receives“32′h0000001a” as the instruction address and the subtractioninstruction “sub r0,r1” as the replacement instruction (step S4200).

Next, the packet address specifying unit 4001 specifies the packetaddress from the upper 29 bits of the instruction address. Theinstruction reading unit 4003 then reads the instruction packet with thespecified packet address from the instruction memory 4004 and stores itin the instruction buffer 4005. In this example, “29′h00000003” isspecified as the packet address, and the instruction sequence “ld(r2),r0∥bra 13′h1fec∥add r2,r3” is stored in the instruction buffer 4005(step S4201).

The in-packet address specifying unit 4002 then specifies the in-packetaddress from the lower 3 bits of the instruction address. In thisexample, the in-packet address “3′b010” is specified (step S4202).

If the specified in-packet address is “3′b000”, the first unit in theinstruction packet in the instruction buffer 4005 is replaced with theinputted replacement instruction. If the specified in-packet address is“3′b010”, the second unit in the instruction packet in the instructionbuffer 4005 is replaced with the inputted replacement instruction. Ifthe specified in-packet address is “3′b100”, the third unit in theinstruction packet in the instruction buffer 4005 is replaced with theinputted replacement instruction. In this example, the specifiedin-packet address is “3′b010”, so that the instruction “bra 13′h1fec” inthe second unit in the instruction packet in the instruction buffer 4005is replaced with the inputted replacement instruction “sub r0,r1”. As aresult, the instruction packet in the instruction buffer 4005 becomes“ld (r2),r0∥sub r0,r1∥add r2,r3” (steps S4203˜S4207).

The instruction writing unit 4014 replaces the instruction packet at theindicated packet address in the instruction memory 4004 with theinstruction packet stored in the instruction buffer 4005. In thisexample, the instruction packet “ld (r2),r0∥bra 13′h1fec∥add r2,r3” atthe packet address “29′h00000003” in the instruction memory 4004 isreplaced with the instruction packet “ld (r2),r0∥sub r0,r1∥add r2,r3” inthe instruction buffer 4005.

As described above, the disassembler of the present embodiment candisassemble instructions that are executable for the processor 309 ofthe first embodiment. When an instruction is disassembled, instead ofjust displaying the PC relative value, the disassembler has the upper PCcalculator and lower PC calculator calculate the address at which thelabel is located, uses the address to search the label table, and sodisplays the appropriate label name.

The debugger of the present embodiment reads instructions from thememory in units of instruction packets that are byte-aligned, rewritesan instruction in the instruction buffer, and writes the instructionsback into the memory in units of instruction packets. This method issuited to the debugging of instructions that are not byte-aligned.

Note that the calculation methods used by the lower PC calculator andthe upper PC calculator do not need to be the carry method described inthe first embodiment, so that another method, such as a separationmethod, an absolute value method, or a linear method, can be used.

The compiler, optimization apparatus, assembler, linker, processor,disassembler, and debugger of the present invention have been explainedby way of the first to eighth embodiments of the present invention,though it should be obvious that the present invention is not limited tothese. Two example modifications are given below.

(1) In the first to sixth embodiments, the assembler code 302, theoptimized code 304, the relocatable codes 306, and the object code 308may be stored in a mask ROM, a semiconductor memory such as flashmemory, a magnetic storage medium such as a floppy disk or a hard disk,or an optical disc such as a CD-ROM or DVD.(2) In the seventh embodiment, the assembler codes 2906 may be stored ina mask ROM, a semiconductor memory such as flash memory, a magneticstorage medium such as a floppy disk or a hard disk, or an optical discsuch as a CD-ROM or DVD.

Although the present invention has been fully described by way ofexamples with reference to accompanying drawings, it is to be noted thatvarious changes and modifications will be apparent to those skilled inthe art. Therefore, unless such changes and modifications depart fromthe scope of the present invention, they should be construed as beingincluded therein.

1. An apparatus comprising: a processor; and an assembler that generatesrelocatable code from an instruction sequence, each address of aninstruction in the instruction sequence having upper bits that indicatea memory address at which a processing packet is stored and lower bitsthat indicate a position of processing target instruction that isincluded in the processing packet, the assembler comprising: a labeldetecting unit configured to detect a label in the instruction sequencethat should be resolved by a difference in addresses between twospecified instructions, and obtaining the addresses of the two specifiedinstructions; a program counter relative value calculating unitconfigured to calculate a program counter relative value by subtractingan address of one of the two specified instructions from an address ofanother of the two specified instructions; and a replacing unitconfigured to replace, using the processor, the label with the programcounter relative value calculated by the program counter relative valuecalculating unit.
 2. The apparatus of claim 1, wherein the programcounter relative value calculating unit includes a lower bit subtractingunit and an upper bit subtracting unit, the lower bit subtracting unitsubtracting lower bits of the address of the one of the two specifiedinstructions from lower bits of the address of the other of the twospecified instructions, for setting a result of a subtraction as lowerbits of the program counter relative value, and sending any carrygenerated in the subtraction it to the upper bit subtracting unit, andthe upper bit subtracting unit subtracting upper bits of the address ofone of the two specified instructions and any carry received from thelower bit subtracting unit from upper bits of the address of the otherof the two specified instructions, and for setting a result of asubtraction as upper bits of the program counter relative value.
 3. Theapparatus of claim 1, wherein the program counter relative valuecalculating unit includes a lower bit subtracting unit and an upper bitsubtracting unit, the lower bit subtracting unit subtracting lower bitsof the address of one of the two specified instructions from lower bitsof the address of the other of the two specified instructions withoutgenerating a carry and setting a result of a subtraction as lower bitsof the program counter relative value, and the upper bit subtractingunit subtracting upper bits of the address of one of the two specifiedinstructions from upper bits of the address of the other of the twospecified instructions, and for setting a result of a subtraction asupper bits of the program counter relative value.
 4. The apparatus ofclaim 1, wherein the program counter relative value calculating unitsubtracts upper bits of an address of one of the two specifiedinstructions from upper bits of an address of the other of the twospecified instructions, sets a result of a subtraction as upper bits ofthe program counter relative value, and sets lower bits of the other ofthe two specified instructions as lower bits of the program counterrelative value.
 5. An apparatus comprising: a processor; and a linkerthat generates object code by combining relocatable code, each addressof an instruction in the relocatable code having upper bits thatindicate a memory address at which a processing packet is stored andlower bits that indicate a position of processing target instructionthat is included in the processing packet, the linker comprising: arelocation information detecting unit configured to detect a label inthe relocatable code that should be resolved by a difference inaddresses between two specified instructions, and obtaining theaddresses of the two specified instructions; a program counter relativevalue calculating unit configured to calculate a program counterrelative value by subtracting an address of one of the two specifiedinstructions from an address of another of the two specifiedinstructions; and a replacing unit configured to replace, using theprocessor, the label with the program counter relative value calculatedby the program counter relative value calculating unit.
 6. The apparatusof claim 5, wherein the program counter relative value calculating unitincludes a lower bit subtracting unit and an upper bit subtracting unit,the lower bit subtracting unit subtracting lower bits of the address ofthe one of the two specified instructions from lower bits of the addressof the other of the two specified instructions, for setting a result ofa subtraction as lower bits of the program counter relative value, andsending any carry generated in the subtraction to the upper bitsubtracting unit, and the upper bit subtracting unit subtracting upperbits of the address of one of the two specified instructions and anycarry received from the lower bit subtracting unit from upper bits ofthe address of the other of the two specified instructions, and forsetting a result of a subtraction as upper bits of the program counterrelative value.
 7. The apparatus of claim 5, wherein the program counterrelative value calculating unit includes a lower bit subtracting unitand an upper bit subtracting unit, the lower bit subtracting unitsubtracting lower bits of the address of one of the two specifiedinstructions from lower bits of the address of the other of the twospecified instructions without generating a carry and setting a resultof a subtraction as lower bits of the program counter relative value,and the upper bit subtracting unit subtracting upper bits of the addressof one of the two specified instructions from upper bits of the addressof the other of the two specified instructions, and for setting a resultof a subtraction as upper bits of the program counter relative value. 8.The apparatus of claim 5, wherein the program counter relative valuecalculating unit subtracts upper bits of an address of one of the twospecified instructions from upper bits of an address of the other of thetwo specified instructions, sets a result of a subtraction as upper bitsof the program counter relative value, and sets lower bits of the otherof the two specified instructions as lower bits of the program counterrelative value.
 9. A non-transitory computer-readable recording mediumstoring an executable assembler program that instructs a processor togenerate relocatable code from optimized code that have been generatedfrom an instruction sequence, each address of an instruction in theoptimized code having upper bits that indicate a memory address at whicha processing packet is stored and lower bits that indicate a position ofprocessing target instruction that is included in the processing packet,the assembler program comprising: a label detecting step for detecting alabel in the instruction sequence that should be resolved by adifference in addresses between two specified instructions, andobtaining the addresses of the two specified instructions; a programcounter relative value calculating step for calculating a programcounter relative value by subtracting an address of one of the twospecified instructions from an address of another of the two specifiedinstructions; and a replacing step for replacing the label with theprogram counter relative value calculated by the program counterrelative value calculating step.
 10. The non-transitorycomputer-readable recording medium of claim 9, wherein the programcounter relative value calculating step includes a lower bit subtractingsubstep and an upper bit subtracting substep, the lower bit subtractingsubstep subtracting lower bits of the address of the one of the twospecified instructions from lower bits of the address of the other ofthe two specified instructions, for setting a result of a subtraction aslower bits of the program counter relative value, and sending any carrygenerated in the subtraction to the upper bit subtracting substep, andthe upper bit subtracting substep subtracting upper bits of the addressof one of the two specified instructions and any carry received from thelower bit subtracting substep from upper bits of the address of theother of the two specified instructions, and for setting a result of asubtraction as upper bits of the program counter relative value.
 11. Thenon-transitory computer-readable recording medium of claim 9, whereinthe program counter relative value calculating step includes a lower bitsubtracting substep and an upper bit subtracting substep, the lower bitsubtracting substep subtracting lower bits of the address of one of thetwo specified instructions from lower bits of the address of the otherof the two specified instructions without generating a carry and settinga result of a subtraction as lower bits of the program counter relativevalue, and the upper bit subtracting substep subtracting upper bits ofthe address of one of the two specified instructions from upper bits ofthe address of the other of the two specified instructions, and forsetting a result of a subtraction as upper bits of the program counterrelative value.
 12. The non-transitory computer-readable recordingmedium of claim 9, wherein the program counter relative valuecalculating step subtracts upper bits of an address of one of the twospecified instructions from upper bits of an address of the other of thetwo specified instructions, sets a result of a subtraction as upper bitsof the program counter relative value, and sets lower bits of the otherof the two specified instructions as lower bits of the program counterrelative value.
 13. A non-transitory computer-readable recording mediumstoring an executable linker program that instructs a processor togenerate object code from relocatable code that has been generated froman instruction sequence, each address of an instruction in the optimizedcode having upper bits that indicate a memory address at which aprocessing packet is stored and lower bits that indicate a position ofprocessing target instruction that is included in the processing packet,the linker program comprising: a relocation information detecting stepfor detecting it a label in the relocatable code that should be resolvedby a difference in addresses between two specified instructions, andobtaining the addresses of the two specified instructions; a programcounter relative value calculating step for calculating a programcounter relative value by subtracting an address of one of the twospecified instructions from an address of another of the two specifiedinstructions; and a replacing step for replacing the label with theprogram counter relative value calculated by the program counterrelative value calculating step.
 14. The non-transitorycomputer-readable recording medium of claim 13, wherein the programcounter relative value calculating step includes a lower bit subtractingsubstep and an upper bit subtracting substep, the lower bit subtractingsubstep subtracting lower bits of the address of the one of the twospecified instructions from lower bits of the address of the other ofthe two specified instructions, for setting a result of a subtraction aslower bits of the program counter relative value, and sending any carrygenerated in the subtraction to the upper bit subtracting substep, andthe upper bit subtracting substep subtracting upper bits of the addressof one of the two specified instructions and any carry received from thelower bit subtracting substep from upper bits of the address of theother of the two specified instructions, and for setting a result of asubtraction as upper bits of the program counter relative value.
 15. Thenon-transitory computer-readable recording medium of claim 13, whereinthe program counter relative value calculating step includes a lower bitsubtracting substep and an upper bit subtracting substep, the lower bitsubtracting substep subtracting lower bits of the address of one of thetwo specified instructions from lower bits of the address of the otherof the two specified instructions without generating a carry and settinga result of a subtraction as lower bits of the program counter relativevalue, and the upper bit subtracting substep subtracting upper bits ofthe address of one of the two specified instructions from upper bits ofthe address of the other of the two specified instructions, and forsetting a result of a subtraction as upper bits of the program counterrelative value.
 16. The non-transitory computer-readable recordingmedium of claim 13, wherein the program counter relative valuecalculating step subtracts upper bits of an address of one of the twospecified instructions from upper bits of an address of the other of thetwo specified instructions, sets a result of a subtraction as upper bitsof the program counter relative value, and sets lower bits of the otherof the two specified instructions as lower bits of the program counterrelative value.